Platelets photochemically treated with amotosalen HCl and ultraviolet A light correct prolonged bleeding times in patients with thrombocytopenia

Evaluation of amotosalen and UVA pathogen-reduced apheresis platelets after 7-day storage

BACKGROUND

Amotosalen/UVA pathogen-reduced platelet components (PRPCs) with storage up to 7 days are standard of care in France, Switzerland, and Austria. PRPCs provide effective hemostasis with reduced risk of transfusion-transmitted infections and transfusion-associated graft versus host disease, reduced wastage and improved availability compared with 5-day-stored PCs. This study evaluated the potency of 7-day PRPCs by in vitro characterization and in vivo pharmacokinetic analysis of autologous PCs.

STUDY DESIGN AND METHODS

The in vitro characteristics of 7-day-stored apheresis PRPCs suspended in 100% plasma or 65% platelet additive solution (PAS-3)/35% plasma, thrombin generation, and in vivo radiolabeled post-transfusion recovery and survival of 7-day-stored PRPCs suspended in 100% plasma were compared with either 7-day-stored or fresh autologous conventional platelets.

RESULTS

PRPCs after 7 days of storage maintained pH, platelet dose, in vitro physiologic characteristics, and thrombin generation when compared to conventional 7-day PCs. In vivo, the mean post-transfusion survival was 151.4 ± 20.1 h for 7-day PRPCs in 100% plasma (Test) versus 209.6 ± 13.9 h for the fresh autologous platelets (Control), (T-ΔC: 72.3 ± 8.8%: 95% confidence interval [CI]: 68.5, 76.1) and mean 24-h post-transfusion recovery 37.6 ± 8.4% for Test versus 56.8 ± 9.2% for Control (T-ΔC: 66.2 ± 11.2%; 95% CI: 61.3, 71.1).

DISCUSSION

PRPCs collected in both 100% plasma as well as 65% PAS-3/35% plasma and stored for 7 days retained in vitro physiologic characteristics. PRPCs stored in 100% plasma for 7 days retained in vivo survival. Lower in vivo post-radiolabeled autologous platelet recovery is consistent with reported reduced count increments for allogenic transfusion.

Efficacy and Safety of Pathogen-Reduced Platelets Compared with Standard Apheresis Platelets: A Systematic Review of RCTs

In this systematic review, we evaluate the efficacy and safety of blood components treated with pathogen reduction technologies (PRTs). We searched the Medline, Embase, Scopus, Ovid, and Cochrane Library to identify RCTs evaluating PRTs. Risk of bias assessment and the Mantel–Haenszel method for data synthesis were used. We included in this review 19 RCTs evaluating 4332 patients (mostly oncohematological patients) receiving blood components treated with three different PRTs. Compared with standard platelets (St-PLTs), the treatment with pathogen-reduced platelets (PR-PLTs) does not increase the occurrence of bleeding events, although a slight increase in the occurrence of severe bleeding events was observed in the overall comparison. No between-groups difference in the occurrence of serious adverse events was observed. PR-PLT recipients had a lower 1 and 24 h CI and CCI. The number of patients with platelet refractoriness and alloimmunization was significantly higher in PR-PLT recipients compared with St-PLT recipients. PR-PLT recipients had a higher number of platelet and RBC transfusions compared with St-PLT recipients, with a shorter transfusion time interval. The quality of evidence for these outcomes was from moderate to high. Blood components treated with PRTs are not implicated in serious adverse events, and PR-PLTs do not have a major effect on the increase in bleeding events. However, treatment with PRTs may require a greater number of transfusions in shorter time intervals and may be implicated in an increase in platelet refractoriness and alloimmunization.

Irradiation of platelets in Transfusion Medicine: risk and benefit judgments

Irradiation of platelet products is generally used to prevent transfusion-associated graft-versus-host disease (TA-GvHD) as well as transfusion-transmitted infections. As an essential prerequisite, gamma-irradiation of blood products prior to transfusion is required in patients who may develop TA-GVHD. Most studies suggest that gamma irradiation has no significant effect on the quality of platelet products; however, more recent studies have shown that the oxidative effects of gamma irradiation can lead to the induction of platelet storage lesion (PSL) and to some extent reduce the efficiency of transfused platelets. As the second widely used irradiation technique, UV-illumination was primarily introduced to reduce the growth of infectious agents during platelet storage, with the advantage that this method can also prevent TA-GvHD. However, the induction of oxidative conditions and platelet pre-activation that lead to PSL is more pronounced after UV-based methods of pathogen reduction. Since these lesions are large enough to clearly affect the post-transfusion platelet recovery and survival, more studies are needed to improve the safety and effectiveness of pathogen reduction technologies (PRTs). Therefore, pointing to other benefits of PRTs, such as preventing TA-GvHD or prolonging the shelf life of products by eliminating the possibility of pathogen growth during storage, does not yet seem to justify their widespread use due to above-mentioned effects. Even for gamma-irradiated platelets, some researchers have suggested that due to decreased 1-hour post-transfusion increments and increased risk of platelet refractoriness, their use should be limited to the patients who may develop TA-GVHD. It is noteworthy that due to the effect of X-rays in preventing TA-GvHD, some recent studies are underway to examine its effects on the quality and effectiveness of platelet products and determine whether X-rays can be used as a more appropriate and cost-effective alternative to gamma radiation. The review presented here provides a detailed description about irradiation-based technologies for platelet products, including their applications, mechanistic features, advantages, and disadvantages.

Pathogen-reduced platelets in pediatric and neonatal patients: Demographics, transfusion rates, and transfusion reactions

BACKGROUND

Pathogen-reduced platelets (PR PLT) are the emerging standard for proactive transfusion-transmitted infection (TTI) mitigation. There is, however, continued hesitation to transfuse PR PLT in children due to limited published data. We report demographics, rates of transfusion, and transfusion reactions (TR) associated with FDA-approved PR PLT in pediatric and neonatal patients at an academic medical center.

METHODS

Retrospective review was performed for patients <18 years receiving at least one platelet over a 300-day period at a large, tertiary care hospital. Patients were transfused PR or conventional (CONV) PLT, based on inventory availability. Statistical analysis was performed using Fisher Exact Test.

RESULTS

During the study period, 191 patients received 1010 platelet transfusions (892 units). Sixty-eight patients received PR PLT only (1.3 units/patient, 95% confidence interval [CI] 1.1-1.5; 1.8 transfusions/patient, 95% CI 1.4-2.2), and 56 patients received CONV PLT only (1.4 units/patient, 95% CI 1.1-1.7; 1.6 transfusions/patient, 95% CI 1.3-1.9). Patients with hematologic malignancies undergoing chemotherapy/radiation and allogeneic hematopoietic stem cell transplant received the most platelet transfusions and more commonly received both platelet types. Of 506 PR PLT units, 5 TRs occurred; 386 CONV PLT resulted in two TRs (p = .7052). Of 51 neonates, 37 received PR PLT without adverse events, including 13 receiving phototherapy. No TTIs were identified in any group.

CONCLUSION

There was no significant difference in rates of transfusion or TRs between PR and CONV PLT. Our study provides additional evidence that PR PLT can be transfused to pediatric and neonatal patients without increasing the risk of acute adverse events.

Platelet Transfusion-Insights from Current Practice to Future Development

Since the late sixties, therapeutic or prophylactic platelet transfusion has been used to relieve hemorrhagic complications of patients with, e.g., thrombocytopenia, platelet dysfunction, and injuries, and is an essential part of the supportive care in high dose chemotherapy. Current and upcoming advances will significantly affect present standards. We focus on specific issues, including the comparison of buffy-coat (BPC) and apheresis platelet concentrates (APC); plasma additive solutions (PAS); further measures for improvement of platelet storage quality; pathogen inactivation; and cold storage of platelets. The objective of this article is to give insights from current practice to future development on platelet transfusion, focusing on these selected issues, which have a potentially major impact on forthcoming guidelines.

A systematic literature review on the use of platelet transfusions in patients with thrombocytopenia

Objective: Investigate globally, current treatment patterns, benefit-risk assessments, humanistic, societal and economic burden of platelet transfusion (PT). Methods: Publications from 1998 to June 27, 2018 were identified, based on databases searches including MEDLINE®; Embase and Cochrane Database of Systematic Reviews. Data from studies meeting pre-specified criteria were extracted and validated by independent reviewers. Data were obtained for efficacy and safety from randomized controlled trials (RCTs); data for epidemiology, treatment patterns, effectiveness, safety, humanistic and societal burden from real-world evidence (RWE) studies; and economic data from both. Results: A total of 3425 abstracts, 194 publications (190 studies) were included. PT use varied widely, from 0%-100% of TCP patients; 1.7%-24.5% in large studies (>1000 patients). Most were used prophylactically rather than therapeutically. 5 of 43 RCTs compared prophylactic PT with no intervention, with mixed results. In RWE studies PT generally increased platelet count (PC). This increase varied by patient characteristics and hence did not always translate into a clinically significant reduction in bleeding risk. Safety concerns included infection risk, alloimmunization and refractoriness with associated cost burden. Discussion: In RCTs and RWE studies there was significant heterogeneity in study design and outcome measures. In RWE studies, patients receiving PT may have been at higher risk than those not receiving PT creating potential bias. There were limited data on humanistic and societal burden. Conclusion: Although PTs are used widely for increasing PC in TCP, it is important to understand the limitations of PTs, and to explore the use of alternative treatment options where available.

Metabolomics study of platelet concentrates photochemically treated with amotosalen and UVA light for pathogen inactivation

BACKGROUND

The risk of bacterial contamination and the deterioration of platelet (PLT) quality limit the shelf-life of platelet concentrates (PCs). The INTERCEPT pathogen inactivation system reduces the risk of pathogen transmission by inhibiting nucleic acid replication using a combination of a photo-reactive compound and UVA illumination. The goal of this study was to investigate the effects the INTERCEPT system has on the PLT metabolome and metabolic activity.

STUDY DESIGN AND METHODS

Paired units of buffy coat-derived PCs were generated using a pool and split strategy (n = 8). The paired PCs were either treated with the INTERCEPT system or left untreated. Samples were collected on Days 1, 2, 4, and 7 of storage. Ultra-performance chromatography coupled with time-of-flight mass spectrometry was used to analyze the extra- and intracellular metabolomes. Constraint-based metabolic modeling was then used to predict the metabolic activity of the stored PLTs.

RESULTS

A relatively large number of metabolites in the extracellular environment were depleted during the processing steps of the INTERCEPT system, in particular, metabolites with hydrophobic functional groups, including acylcarnitines and lysophosphatidylcholines. In the intracellular environment, alterations in glucose and glycerophospholipid metabolism and decreased levels of 2-hydroxyglutarate were observed following the INTERCEPT treatment. Untargeted metabolomics analysis revealed residual amotosalen dimers present in the treated PCs. Systems-level analysis of PLT metabolism indicated that the INTERCEPT system does not have a significant impact on the PLT energy metabolism and nutrient utilization.

CONCLUSIONS

The INTERCEPT system significantly alters the metabolome of the stored PCs without significantly influencing PLT energy metabolism.

Pathogen inactivation with amotosalen plus UVA illumination minimally impacts microRNA expression in platelets during storage under standard blood banking conditions

BACKGROUND

To reduce the risk of transfusion transmission infection, nucleic acid targeted methods have been developed to inactivate pathogens in PCs. miRNAs have been shown to play an important role in platelet function, and changes in the abundance of specific miRNAs during storage have been observed, as have perturbation effects related to pathogen inactivation (PI) methods. The aim of this work was to investigate the effects of PI on selected miRNAs during storage.

STUDY DESIGN AND METHODS

Using a pool and split strategy, 3 identical buffy coat PC units were generated from a pool of 24 whole blood donors. Each unit received a different treatment: 1) Untreated platelet control in platelet additive solution (C-PAS); 2) Amotosalen-UVA-treated platelets in PAS (PI-PAS); and 3) untreated platelets in donor plasma (U-PL). PCs were stored for 7 days under standard blood banking conditions. Standard platelet quality control (QC) parameters and 25 selected miRNAs were analyzed.

RESULTS

During the 7-day storage period, differences were found in several QC parameters relating to PI treatment and storage in plasma, but overall the three treatments were comparable. Out of 25 miRNA tested changes in regulation of 5 miRNA in PI-PAS and 3 miRNA U-PL where detected compared to C-PAS. A statistically significant difference was observed in down regulations miR-96-5p on Days 2 and 4, 61.9% and 61.8%, respectively, in the PI-PAS treatment.

CONCLUSION

Amotosalen-UVA treatment does not significantly alter the miRNA profile of platelet concentrates generated and stored using standard blood banking conditions.

Influence of platelet preparation techniques on in vitro storage quality after psoralen-based photochemical treatment using new processing sets for triple-dose units

BACKGROUND

The INTERCEPT Blood System (IBS) for platelets (PLTs) uses a combination of psoralen and ultraviolet-A light to inactivate pathogens that may contaminate PLT concentrates (PCs). However, no data are available on the quality of IBS-treated PLTs from different apheresis and buffy-coat PC preparation platforms using the new triple storage (TS) set.

STUDY DESIGN AND METHODS

The objective of this study was to evaluate the TS set on three different preparation platforms compared with the large-volume (LV) set, as control. PLT in vitro metabolic and activation parameters were studied over 7 days.

RESULTS

Several statistical differences are observed between the two sets, particularly for pH, oxygen pressure (pO₂ ), carbonic gaz pressure (pCO₂ ), and bicarbonate. The three different preparation techniques influence PLT parameters, and the difference is statistically significant for all the studied parameters, except for pCO₂ . The TS set has the advantage of shorter compound adsorption device time, higher PLT recoveries, and less PLT activation.

CONCLUSION

Results from the measured metabolic parameters and PLT variables obtained from PCs treated by LV and TS sets indicated good PLT function preservation up to 7 days of storage. The in vitro assessment results demonstrated acceptable PLT function for transfusion.

Pathogen-reduced platelets for the prevention of bleeding

BACKGROUND

Platelet transfusions are used to prevent and treat bleeding in people who are thrombocytopenic. Despite improvements in donor screening and laboratory testing, a small risk of viral, bacterial, or protozoal contamination of platelets remains. There is also an ongoing risk from newly emerging blood transfusion-transmitted infections for which laboratory tests may not be available at the time of initial outbreak.One solution to reduce the risk of blood transfusion-transmitted infections from platelet transfusion is photochemical pathogen reduction, in which pathogens are either inactivated or significantly depleted in number, thereby reducing the chance of transmission. This process might offer additional benefits, including platelet shelf-life extension, and negate the requirement for gamma-irradiation of platelets. Although current pathogen-reduction technologies have been proven to reduce pathogen load in platelet concentrates, a number of published clinical studies have raised concerns about the effectiveness of pathogen-reduced platelets for post-transfusion platelet count recovery and the prevention of bleeding when compared with standard platelets.This is an update of a Cochrane review first published in 2013.

OBJECTIVES

To assess the effectiveness of pathogen-reduced platelets for the prevention of bleeding in people of any age requiring platelet transfusions.

SEARCH METHODS

We searched for randomised controlled trials (RCTs) in the Cochrane Central Register of Controlled Trials (CENTRAL) (the Cochrane Library 2016, Issue 9), MEDLINE (from 1946), Embase (from 1974), CINAHL (from 1937), the Transfusion Evidence Library (from 1950), and ongoing trial databases to 24 October 2016.

SELECTION CRITERIA

We included RCTs comparing the transfusion of pathogen-reduced platelets with standard platelets, or comparing different types of pathogen-reduced platelets.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures expected by Cochrane.

MAIN RESULTS

We identified five new trials in this update of the review. A total of 15 trials were eligible for inclusion in this review, 12 completed trials (2075 participants) and three ongoing trials. Ten of the 12 completed trials were included in the original review. We did not identify any RCTs comparing the transfusion of one type of pathogen-reduced platelets with another.Nine trials compared Intercept® pathogen-reduced platelets to standard platelets, two trials compared Mirasol® pathogen-reduced platelets to standard platelets; and one trial compared both pathogen-reduced platelets types to standard platelets. Three RCTs were randomised cross-over trials, and nine were parallel-group trials. Of the 2075 participants enrolled in the trials, 1981 participants received at least one platelet transfusion (1662 participants in Intercept® platelet trials and 319 in Mirasol® platelet trials).One trial included children requiring cardiac surgery (16 participants) or adults requiring a liver transplant (28 participants). All of the other participants were thrombocytopenic individuals who had a haematological or oncological diagnosis. Eight trials included only adults.Four of the included studies were at low risk of bias in every domain, while the remaining eight included studies had some threats to validity.Overall, the quality of the evidence was low to high across different outcomes according to GRADE methodology.We are very uncertain as to whether pathogen-reduced platelets increase the risk of any bleeding (World Health Organization (WHO) Grade 1 to 4) (5 trials, 1085 participants; fixed-effect risk ratio (RR) 1.09, 95% confidence interval (CI) 1.02 to 1.15; I2 = 59%, random-effect RR 1.14, 95% CI 0.93 to 1.38; I2 = 59%; low-quality evidence).There was no evidence of a difference between pathogen-reduced platelets and standard platelets in the incidence of clinically significant bleeding complications (WHO Grade 2 or higher) (5 trials, 1392 participants; RR 1.10, 95% CI 0.97 to 1.25; I2 = 0%; moderate-quality evidence), and there is probably no difference in the risk of developing severe bleeding (WHO Grade 3 or higher) (6 trials, 1495 participants; RR 1.24, 95% CI 0.76 to 2.02; I2 = 32%; moderate-quality evidence).There is probably no difference between pathogen-reduced platelets and standard platelets in the incidence of all-cause mortality at 4 to 12 weeks (6 trials, 1509 participants; RR 0.81, 95% CI 0.50 to 1.29; I2 = 26%; moderate-quality evidence).There is probably no difference between pathogen-reduced platelets and standard platelets in the incidence of serious adverse events (7 trials, 1340 participants; RR 1.09, 95% CI 0.88 to 1.35; I2 = 0%; moderate-quality evidence). However, no bacterial transfusion-transmitted infections occurred in the six trials that reported this outcome.Participants who received pathogen-reduced platelet transfusions had an increased risk of developing platelet refractoriness (7 trials, 1525 participants; RR 2.94, 95% CI 2.08 to 4.16; I2 = 0%; high-quality evidence), though the definition of platelet refractoriness differed between trials.Participants who received pathogen-reduced platelet transfusions required more platelet transfusions (6 trials, 1509 participants; mean difference (MD) 1.23, 95% CI 0.86 to 1.61; I2 = 27%; high-quality evidence), and there was probably a shorter time interval between transfusions (6 trials, 1489 participants; MD -0.42, 95% CI -0.53 to -0.32; I2 = 29%; moderate-quality evidence). Participants who received pathogen-reduced platelet transfusions had a lower 24-hour corrected-count increment (7 trials, 1681 participants; MD -3.02, 95% CI -3.57 to -2.48; I2 = 15%; high-quality evidence).None of the studies reported quality of life.We did not evaluate any economic outcomes.There was evidence of subgroup differences in multiple transfusion trials between the two pathogen-reduced platelet technologies assessed in this review (Intercept® and Mirasol®) for all-cause mortality and the interval between platelet transfusions (favouring Intercept®).

AUTHORS' CONCLUSIONS

Findings from this review were based on 12 trials, and of the 1981 participants who received a platelet transfusion only 44 did not have a haematological or oncological diagnosis.In people with haematological or oncological disorders who are thrombocytopenic due to their disease or its treatment, we found high-quality evidence that pathogen-reduced platelet transfusions increase the risk of platelet refractoriness and the platelet transfusion requirement. We found moderate-quality evidence that pathogen-reduced platelet transfusions do not affect all-cause mortality, the risk of clinically significant or severe bleeding, or the risk of a serious adverse event. There was insufficient evidence for people with other diagnoses.All three ongoing trials are in adults (planned recruitment 1375 participants) with a haematological or oncological diagnosis.

Platelet concentrates: Balancing between efficacy and safety?

Platelet transfusions continue to be the mainstay to treat patients with quantitative and qualitative platelet disorders. Each year, about 10 millions of platelet transfusions are administered to patients worldwide with marked differences in usage between regions depending on socioeconomic development of the countries. Unfortunately, its use is associated to immune and non-immune side effects. Among the non-immune, bacterial contamination is still the major infectious risk. When bacterial culture methods are introduced for preventing bacterial septic reactions it has been found that this strategy reduce to one half the septic reactions, but do not eliminate completely that risk. To remove completely the risk, a new bacteria detection test at the time of issuance in the case of platelets stored for four or five days would be needed. Pathogen inactivation (PI) methods already in the market (based in the addition of amotosalen (A-L) or riboflavin (R-L) and the illumination with ultraviolet light) or under development (ultraviolet light C and agitation) have shown to be efficacious in the inactivation of bacteria and no cases of septic reactions associated to a pathogen-reduced product has been identified. However, it has been shown that PI technologies have measurable effects on platelet in vitro parameters and reduce the recovery and survival of treated platelets in vivo. Although these effects do not hamper the hemostatic capacity of treated platelets, an increased usage associated with PI technologies has been reported. This increase in utilization seems to be the toll to be paid if we want to completely eliminate the risk of bacterial sepsis in the recipients of platelet transfusion.

Recent Advances in Preventing Adverse Reactions to Transfusion

The spectrum of adverse reactions to blood product transfusion ranges from a benign clinical course to serious morbidity and mortality.  There have been many advances in technologies and transfusion strategies to decrease the risk of adverse reactions. Our aim is to address a few of the advancements in increasing the safety of the blood supply, specifically pathogen reduction technologies, bacterial contamination risk reduction, and transfusion associated acute lung injury risk mitigation strategies.

Comparison of different platelet count thresholds to guide administration of prophylactic platelet transfusion for preventing bleeding in people with haematological disorders after myelosuppressive chemotherapy or stem cell transplantation

BACKGROUND

Platelet transfusions are used in modern clinical practice to prevent and treat bleeding in people who are thrombocytopenic due to bone marrow failure. Although considerable advances have been made in platelet transfusion therapy in the last 40 years, some areas continue to provoke debate, especially concerning the use of prophylactic platelet transfusions for the prevention of thrombocytopenic bleeding.This is an update of a Cochrane review first published in 2004, and previously updated in 2012 that addressed four separate questions: prophylactic versus therapeutic-only platelet transfusion policy; prophylactic platelet transfusion threshold; prophylactic platelet transfusion dose; and platelet transfusions compared to alternative treatments. This review has now been split into four smaller reviews looking at these questions individually; this review compares prophylactic platelet transfusion thresholds.

OBJECTIVES

To determine whether different platelet transfusion thresholds for administration of prophylactic platelet transfusions (platelet transfusions given to prevent bleeding) affect the efficacy and safety of prophylactic platelet transfusions in preventing bleeding in people with haematological disorders undergoing myelosuppressive chemotherapy or haematopoietic stem cell transplantation (HSCT).

SEARCH METHODS

We searched for randomised controlled trials (RCTs) in the Cochrane Central Register of Controlled Trials (CENTRAL) (Cochrane Library 2015, Issue 6, 23 July 2015), MEDLINE (from 1946), Embase (from 1974), CINAHL (from 1937), the Transfusion Evidence Library (from 1950), and ongoing trial databases to 23 July 2015.

SELECTION CRITERIA

We included RCTs involving transfusions of platelet concentrates, prepared either from individual units of whole blood or by apheresis, and given to prevent bleeding in people with haematological disorders (receiving myelosuppressive chemotherapy or undergoing HSCT) that compared different thresholds for administration of prophylactic platelet transfusions (low trigger (5 x 10(9)/L); standard trigger (10 x 10(9)/L); higher trigger (20 x 10(9)/L, 30 x 10(9)/L, 50 x 10(9)/L); or alternative platelet trigger (for example platelet mass)).

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures expected by Cochrane.

MAIN RESULTS

Three trials met our predefined inclusion criteria and were included for analysis in the review (499 participants). All three trials compared a standard trigger (10 x 10(9)/L) versus a higher trigger (20 x 10(9)/L or 30 x 10(9)/L). None of the trials compared a low trigger versus a standard trigger or an alternative platelet trigger. The trials were conducted between 1991 and 2001 and enrolled participants from fairly comparable patient populations.The original review contained four trials (658 participants); in the previous update of this review we excluded one trial (159 participants) because fewer than 80% of participants had a haematological disorder. We identified no new trials in this update of the review.Overall, the methodological quality of the studies was low across different outcomes according to GRADE methodology. None of the included studies were at low risk of bias in every domain, and all the included studies had some threats to validity.Three studies reported the number of participants with at least one clinically significant bleeding episode within 30 days from the start of the study. There was no evidence of a difference in the number of participants with a clinically significant bleeding episode between the standard and higher trigger groups (three studies; 499 participants; risk ratio (RR) 1.35, 95% confidence interval (CI) 0.95 to 1.90; low-quality evidence).One study reported the number of days with a clinically significant bleeding event (adjusted for repeated measures). There was no evidence of a difference in the number of days of bleeding per participant between the standard and higher trigger groups (one study; 255 participants; relative proportion of days with World Health Organization Grade 2 or worse bleeding (RR 1.71, 95% CI 0.84 to 3.48, P = 0.162; authors' own results; low-quality evidence).Two studies reported the number of participants with severe or life-threatening bleeding. There was no evidence of any difference in the number of participants with severe or life-threatening bleeding between a standard trigger level and a higher trigger level (two studies; 421 participants; RR 0.99, 95% CI 0.52 to 1.88; low-quality evidence).Only one study reported the time to first bleeding episode. There was no evidence of any difference in the time to the first bleeding episode between a standard trigger level and a higher trigger level (one study; 255 participants; hazard ratio 1.11, 95% CI 0.64 to 1.91; low-quality evidence).Only one study reported on all-cause mortality within 30 days from the start of the study. There was no evidence of any difference in all-cause mortality between standard and higher trigger groups (one study; 255 participants; RR 1.78, 95% CI 0.83 to 3.81; low-quality evidence).Three studies reported on the number of platelet transfusions per participant. Two studies reported on the mean number of platelet transfusions per participant. There was a significant reduction in the number of platelet transfusions per participant in the standard trigger group (two studies, mean difference -2.09, 95% CI -3.20 to -0.99; low-quality evidence).One study reported on the number of transfusion reactions. There was no evidence to demonstrate any difference in transfusion reactions between the standard and higher trigger groups (one study; 79 participants; RR 0.07, 95% CI 0.00 to 1.09).None of the studies reported on quality of life.

AUTHORS' CONCLUSIONS

In people with haematological disorders who are thrombocytopenic due to myelosuppressive chemotherapy or HSCT, we found low-quality evidence that a standard trigger level (10 x 10(9)/L) is associated with no increase in the risk of bleeding when compared to a higher trigger level (20 x 10(9)/L or 30 x 10(9)/L). There was low-quality evidence that a standard trigger level is associated with a decreased number of transfusion episodes when compared to a higher trigger level (20 x 10(9)/L or 30 x 10(9)/L).Findings from this review were based on three studies and 499 participants. Without further evidence, it is reasonable to continue with the current practice of administering prophylactic platelet transfusions using the standard trigger level (10 x 10(9)/L) in the absence of other risk factors for bleeding.

Different doses of prophylactic platelet transfusion for preventing bleeding in people with haematological disorders after myelosuppressive chemotherapy or stem cell transplantation

BACKGROUND

Platelet transfusions are used in modern clinical practice to prevent and treat bleeding in people who are thrombocytopenic due to bone marrow failure. Although considerable advances have been made in platelet transfusion therapy in the last 40 years, some areas continue to provoke debate, especially concerning the use of prophylactic platelet transfusions for the prevention of thrombocytopenic bleeding.This is an update of a Cochrane review first published in 2004, and updated in 2012 that addressed four separate questions: prophylactic versus therapeutic-only platelet transfusion policy; prophylactic platelet transfusion threshold; prophylactic platelet transfusion dose; and platelet transfusions compared to alternative treatments. This review has now been split into four smaller reviews; this review compares different platelet transfusion doses.

OBJECTIVES

To determine whether different doses of prophylactic platelet transfusions (platelet transfusions given to prevent bleeding) affect their efficacy and safety in preventing bleeding in people with haematological disorders undergoing myelosuppressive chemotherapy with or without haematopoietic stem cell transplantation (HSCT).

SEARCH METHODS

We searched for randomised controlled trials in the Cochrane Central Register of Controlled Trials (CENTRAL) (Cochrane Library 2015, Issue 6), MEDLINE (from 1946), Embase (from 1974), CINAHL (from 1937), the Transfusion Evidence Library (from 1950), and ongoing trial databases to 23 July 2015.

SELECTION CRITERIA

Randomised controlled trials involving transfusions of platelet concentrates, prepared either from individual units of whole blood or by apheresis, and given to prevent bleeding in people with malignant haematological disorders or undergoing HSCT that compared different platelet component doses (low dose 1.1 x 10(11)/m(2) ± 25%, standard dose 2.2 x 10(11)/m(2) ± 25%, high dose 4.4 x 10(11)/m(2) ± 25%).

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures expected by The Cochrane Collaboration.

MAIN RESULTS

We included seven trials (1814 participants) in this review; six were conducted during one course of treatment (chemotherapy or HSCT).Overall the methodological quality of studies was low to moderate across different outcomes according to GRADE methodology. None of the included studies were at low risk of bias in every domain, and all the included studies had some threats to validity.Five studies reported the number of participants with at least one clinically significant bleeding episode within 30 days from the start of the study. There was no difference in the number of participants with a clinically significant bleeding episode between the low-dose and standard-dose groups (four studies; 1170 participants; risk ratio (RR) 1.04, 95% confidence interval (CI) 0.95 to 1.13; moderate-quality evidence); low-dose and high-dose groups (one study; 849 participants; RR 1.02, 95% CI 0.93 to 1.11; moderate-quality evidence); or high-dose and standard-dose groups (two studies; 951 participants; RR 1.02, 95% CI 0.93 to 1.11; moderate-quality evidence).Three studies reported the number of days with a clinically significant bleeding event per participant. There was no difference in the number of days of bleeding per participant between the low-dose and standard-dose groups (two studies; 230 participants; mean difference -0.17, 95% CI -0.51 to 0.17; low quality evidence). One study (855 participants) showed no difference in the number of days of bleeding per participant between high-dose and standard-dose groups, or between low-dose and high-dose groups (849 participants).Three studies reported the number of participants with severe or life-threatening bleeding. There was no difference in the number of participants with severe or life-threatening bleeding between a low-dose and a standard-dose platelet transfusion policy (three studies; 1059 participants; RR 1.33, 95% CI 0.91 to 1.92; low-quality evidence); low-dose and high-dose groups (one study; 849 participants; RR 1.20, 95% CI 0.82 to 1.77; low-quality evidence); or high-dose and standard-dose groups (one study; 855 participants; RR 1.11, 95% CI 0.73 to 1.68; low-quality evidence).Two studies reported the time to first bleeding episodes; we were unable to perform a meta-analysis. Both studies (959 participants) individually found that the time to first bleeding episode was either the same, or longer, in the low-dose group compared to the standard-dose group. One study (855 participants) found that the time to the first bleeding episode was the same in the high-dose group compared to the standard-dose group.Three studies reported all-cause mortality within 30 days from the start of the study. There was no difference in all-cause mortality between treatment arms (low-dose versus standard-dose: three studies; 1070 participants; RR 2.04, 95% CI 0.70 to 5.93; low-quality evidence; low-dose versus high-dose: one study; 849 participants; RR 1.33, 95% CI 0.50 to 3.54; low-quality evidence; and high-dose versus standard-dose: one study; 855 participants; RR 1.71, 95% CI 0.51 to 5.81; low-quality evidence).Six studies reported the number of platelet transfusions; we were unable to perform a meta-analysis. Two studies (959 participants) out of three (1070 participants) found that a low-dose transfusion strategy led to more transfusion episodes than a standard-dose. One study (849 participants) found that a low-dose transfusion strategy led to more transfusion episodes than a high-dose strategy. One study (855 participants) out of three (1007 participants) found no difference in the number of platelet transfusions between the high-dose and standard-dose groups.One study reported on transfusion reactions. This study's authors suggested that a high-dose platelet transfusion strategy may lead to a higher rate of transfusion-related adverse events.None of the studies reported quality-of-life.

AUTHORS' CONCLUSIONS

In haematology patients who are thrombocytopenic due to myelosuppressive chemotherapy or HSCT, we found no evidence to suggest that a low-dose platelet transfusion policy is associated with an increased bleeding risk compared to a standard-dose or high-dose policy, or that a high-dose platelet transfusion policy is associated with a decreased risk of bleeding when compared to a standard-dose policy.A low-dose platelet transfusion strategy leads to an increased number of transfusion episodes compared to a standard-dose strategy. A high-dose platelet transfusion strategy does not decrease the number of transfusion episodes per participant compared to a standard-dose regimen, and it may increase the number of transfusion-related adverse events.Findings from this review would suggest a change from current practice, with low-dose platelet transfusions used for people receiving in-patient treatment for their haematological disorder and high-dose platelet transfusion strategies not being used routinely.

A therapeutic-only versus prophylactic platelet transfusion strategy for preventing bleeding in patients with haematological disorders after myelosuppressive chemotherapy or stem cell transplantation

BACKGROUND

Platelet transfusions are used in modern clinical practice to prevent and treat bleeding in thrombocytopenic patients with bone marrow failure. Although considerable advances have been made in platelet transfusion therapy in the last 40 years, some areas continue to provoke debate, especially concerning the use of prophylactic platelet transfusions for the prevention of thrombocytopenic bleeding.This is an update of a Cochrane review first published in 2004 and updated in 2012 that addressed four separate questions: therapeutic-only versus prophylactic platelet transfusion policy; prophylactic platelet transfusion threshold; prophylactic platelet transfusion dose; and platelet transfusions compared to alternative treatments. We have now split this review into four smaller reviews looking at these questions individually; this review is the first part of the original review.

OBJECTIVES

To determine whether a therapeutic-only platelet transfusion policy (platelet transfusions given when patient bleeds) is as effective and safe as a prophylactic platelet transfusion policy (platelet transfusions given to prevent bleeding, usually when the platelet count falls below a given trigger level) in patients with haematological disorders undergoing myelosuppressive chemotherapy or stem cell transplantation.

SEARCH METHODS

We searched for randomised controlled trials (RCTs) in the Cochrane Central Register of Controlled Trials (Cochrane Library 2015, Issue 6), MEDLINE (from 1946), Embase (from 1974), CINAHL (from 1937), the Transfusion Evidence Library (from 1950) and ongoing trial databases to 23 July 2015.

SELECTION CRITERIA

RCTs involving transfusions of platelet concentrates prepared either from individual units of whole blood or by apheresis, and given to prevent or treat bleeding in patients with malignant haematological disorders receiving myelosuppressive chemotherapy or undergoing HSCT.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by The Cochrane Collaboration.

MAIN RESULTS

We identified seven RCTs that compared therapeutic platelet transfusions to prophylactic platelet transfusions in haematology patients undergoing myelosuppressive chemotherapy or HSCT. One trial is still ongoing, leaving six trials eligible with a total of 1195 participants. These trials were conducted between 1978 and 2013 and enrolled participants from fairly comparable patient populations. We were able to critically appraise five of these studies, which contained separate data for each arm, and were unable to perform quantitative analysis on one study that did not report the numbers of participants in each treatment arm.Overall the quality of evidence per outcome was low to moderate according to the GRADE approach. None of the included studies were at low risk of bias in every domain, and all the studies identified had some threats to validity. We deemed only one study to be at low risk of bias in all domains other than blinding.Two RCTs (801 participants) reported at least one bleeding episode within 30 days of the start of the study. We were unable to perform a meta-analysis due to considerable statistical heterogeneity between studies. The statistical heterogeneity seen may relate to the different methods used in studies for the assessment and grading of bleeding. The underlying patient diagnostic and treatment categories also appeared to have some effect on bleeding risk. Individually these studies showed a similar effect, that a therapeutic-only platelet transfusion strategy was associated with an increased risk of clinically significant bleeding compared with a prophylactic platelet transfusion policy. Number of days with a clinically significant bleeding event per participant was higher in the therapeutic-only group than in the prophylactic group (one RCT; 600 participants; mean difference 0.50, 95% confidence interval (CI) 0.10 to 0.90; moderate-quality evidence). There was insufficient evidence to determine whether there was any difference in the number of participants with severe or life-threatening bleeding between a therapeutic-only transfusion policy and a prophylactic platelet transfusion policy (two RCTs; 801 participants; risk ratio (RR) 4.91, 95% CI 0.86 to 28.12; low-quality evidence). Two RCTs (801 participants) reported time to first bleeding episode. As there was considerable heterogeneity between the studies, we were unable to perform a meta-analysis. Both studies individually found that time to first bleeding episode was shorter in the therapeutic-only group compared with the prophylactic platelet transfusion group.There was insufficient evidence to determine any difference in all-cause mortality within 30 days of the start of the study using a therapeutic-only platelet transfusion policy compared with a prophylactic platelet transfusion policy (two RCTs; 629 participants). Mortality was a rare event, and therefore larger studies would be needed to establish the effect of these alternative strategies. There was a clear reduction in the number of platelet transfusions per participant in the therapeutic-only arm (two RCTs, 991 participants; standardised mean reduction of 0.50 platelet transfusions per participant, 95% CI -0.63 to -0.37; moderate-quality evidence). None of the studies reported quality of life. There was no evidence of any difference in the frequency of adverse events, such as transfusion reactions, between a therapeutic-only and prophylactic platelet transfusion policy (two RCTs; 991 participants; RR 1.02, 95% CI 0.62 to 1.68), although the confidence intervals were wide.

AUTHORS' CONCLUSIONS

We found low- to moderate-grade evidence that a therapeutic-only platelet transfusion policy is associated with increased risk of bleeding when compared with a prophylactic platelet transfusion policy in haematology patients who are thrombocytopenic due to myelosuppressive chemotherapy or HSCT. There is insufficient evidence to determine any difference in mortality rates and no evidence of any difference in adverse events between a therapeutic-only platelet transfusion policy and a prophylactic platelet transfusion policy. A therapeutic-only platelet transfusion policy is associated with a clear reduction in the number of platelet components administered.

Pathogen inactivation technologies for cellular blood components: an update

Nowadays patients receiving blood components are exposed to much less transfusion-transmitted infectious diseases than three decades before when among others HIV was identified as causative agent for the acquired immunodeficiency syndrome and the transmission by blood or coagulation factors became evident. Since that time the implementation of measures for risk prevention and safety precaution was socially and politically accepted. Currently emerging pathogens like arboviruses and the well-known bacterial contamination of platelet concentrates still remain major concerns of blood safety with important clinical consequences, but very rarely with fatal outcome for the blood recipient. In contrast to the well-established pathogen inactivation strategies for fresh frozen plasma using the solvent-detergent procedure or methylene blue and visible light, the bench-to-bedside translation of novel pathogen inactivation technologies for cell-containing blood components such as platelets and red blood cells are still underway. This review summarizes the pharmacological/toxicological assessment and the inactivation efficacy against viruses, bacteria, and protozoa of each of the currently available pathogen inactivation technologies and highlights the impact of the results obtained from several randomized clinical trials and hemovigilance data. Until now in some European countries pathogen inactivation technologies are in in routine use for single-donor plasma and platelets. The invention and adaption of pathogen inactivation technologies for red blood cell units and whole blood donations suggest the universal applicability of these technologies and foster a paradigm shift in the manufacturing of safe blood.

Preserved functional and biochemical characteristics of platelet components prepared with amotosalen and ultraviolet A for pathogen inactivation

BACKGROUND

Platelet concentrate (PC) functionality decreases during storage. This is referred to as the storage lesion. Pathogen inactivation may accelerate or induce lesions, potentially accounting for reduced viability. Our aim was to characterize functional and biochemical properties of platelets (PLTs) from photochemically treated buffy-coat PCs (PCT-PCs) compared to those from conventional PCs.

STUDY DESIGN AND METHODS

Four PCT-PCs and four conventional PCs were stored for 6.5 days and PLT function and proteomic profiles were examined at various time points during storage. To evaluate their intrinsic properties, samples of stored PLTs were taken, washed, and suspended in Tyrode's buffer before testing.

RESULTS

PLT counts and morphology were conserved although a slight increase in the PLT volume was observed after PCT. Glycoprotein (GP) IIbIIIa, IaIIa, and VI expression remained stable while GPIbα declined similarly in both types of PCs. A steep decrease (50%) in GPV occurred on Day 1.5 in PCT-PCs and Day 2.5 in control PCs. For both PCT- and control PCs, P-selectin expression and activated GPIIbIIIa remained low during storage. PCT- and control PCs were fully responsive to aggregation agonists up to Day 4.5 and exhibited similar perfusion functionality. Mitochondrial membrane potential and annexin A5 binding of PCT-PCs and control PCs were comparable. Two-dimensional differential in-gel electrophoresis and mass spectrometry profiles for 1882 protein spots revealed only three proteins selectively changed in PCT-PCs compared to control-PCs.

CONCLUSION

Washed treated and untreated PCs have similar functional, morphologic, and proteomic characteristics provided that PLTs are suspended in an appropriate medium during testing.

Pathogen-reduced platelets for the prevention of bleeding

BACKGROUND

Platelet transfusions are used to prevent and treat bleeding in patients who are thrombocytopenic. Despite improvements in donor screening and laboratory testing, a small risk of viral, bacterial or protozoal contamination of platelets remains. There is also an ongoing risk from newly emerging blood transfusion-transmitted infections (TTIs) for which laboratory tests may not be available at the time of initial outbreak.One solution to reduce further the risk of TTIs from platelet transfusion is photochemical pathogen reduction, a process by which pathogens are either inactivated or significantly depleted in number, thereby reducing the chance of transmission. This process might offer additional benefits, including platelet shelf-life extension, and negate the requirement for gamma-irradiation of platelets. Although current pathogen-reduction technologies have been proven significantly to reduce pathogen load in platelet concentrates, a number of published clinical studies have raised concerns about the effectiveness of pathogen-reduced platelets for post-transfusion platelet recovery and the prevention of bleeding when compared with standard platelets.

OBJECTIVES

To assess the effectiveness of pathogen-reduced platelets for the prevention of bleeding in patients requiring platelet transfusions.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library 2013, Issue 1), MEDLINE (1950 to 18 February 2013), EMBASE (1980 to 18 February 2013), CINAHL (1982 to 18 February 2013) and the Transfusion Evidence Library (1980 to 18 February 2013). We also searched several international and ongoing trial databases and citation-tracked relevant reference lists. We requested information on possible unpublished trials from known investigators in the field.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing the transfusion of pathogen-reduced platelets with standard platelets. We did not identify any RCTs which compared the transfusion of one type of pathogen-reduced platelets with another.

DATA COLLECTION AND ANALYSIS

One author screened all references, excluding duplicates and those clearly irrelevant. Two authors then screened the remaining references, confirmed eligibility, extracted data and analysed trial quality independently. We requested and obtained a significant amount of missing data from trial authors. We performed meta-analyses where appropriate using the fixed-effect model for risk ratios (RR) or mean differences (MD), with 95% confidence intervals (95% CI), and used the I² statistic to explore heterogeneity, employing the random-effects model when I² was greater than 30%.

MAIN RESULTS

We included 10 trials comparing pathogen-reduced platelets with standard platelets. Nine trials assessed Intercept® pathogen-reduced platelets and one trial Mirasol® pathogen-reduced platelets. Two were randomised cross-over trials and the remaining eight were parallel-group RCTs. In total, 1422 participants were available for analysis across the 10 trials, of which 675 participants received Intercept® and 56 Mirasol® platelet transfusions. Four trials assessed the response to a single study platelet transfusion (all Intercept®) and six to multiple study transfusions (Intercept® (N = 5), Mirasol® (N = 1)) compared with standard platelets.We found the trials to be generally at low risk of bias but heterogeneous regarding the nature of the interventions (platelet preparation), protocols for platelet transfusion, definitions of outcomes, methods of outcome assessment and duration of follow-up.Our primary outcomes were mortality, 'any bleeding', 'clinically significant bleeding' and 'severe bleeding', and were grouped by duration of follow-up: short (up to 48 hours), medium (48 hours to seven days) or long (more than seven days). Meta-analysis of data from five trials of multiple platelet transfusions reporting 'any bleeding' over a long follow-up period found an increase in bleeding in those receiving pathogen-reduced platelets compared with standard platelets using the fixed-effect model (RR 1.09, 95% CI 1.02 to 1.15, I² = 59%); however, this meta-analysis showed no difference between treatment arms when using the random-effects model (RR 1.14, 95% CI 0.93 to 1.38).There was no evidence of a difference between treatment arms in the number of patients with 'clinically significant bleeding' (reported by four out of the same five trials) or 'severe bleeding' (reported by all five trials) (respectively, RR 1.06, 95% CI 0.93 to 1.21, I² = 2%; RR 1.27, 95% CI 0.76 to 2.12, I² = 51%). We also found no evidence of a difference between treatment arms for all-cause mortality, acute transfusion reactions, adverse events, serious adverse events and red cell transfusion requirements in the trials which reported on these outcomes. No bacterial transfusion-transmitted infections occurred in the six trials that reported this outcome.Although the definition of platelet refractoriness differed between trials, the relative risk of this event was 2.74 higher following pathogen-reduced platelet transfusion (RR 2.74, 95% CI 1.84 to 4.07, I² = 0%). Participants required 7% more platelet transfusions following pathogen-reduced platelet transfusion when compared with standard platelet transfusion (MD 0.07, 95% CI 0.03 to 0.11, I² = 21%), although the interval between platelet transfusions was only shown to be significantly shorter following multiple Intercept® pathogen-reduced platelet transfusion when compared with standard platelet transfusion (MD -0.51, 95% CI -0.66 to -0.37, I² = 0%). In trials of multiple pathogen-reduced platelets, our analyses showed the one- and 24-hour count and corrected count increments to be significantly inferior to standard platelets. However, one-hour increments were similar in trials of single platelet transfusions, although the 24-hour count and corrected count increments were again significantly lower.

AUTHORS' CONCLUSIONS

We found no evidence of a difference in mortality, 'clinically significant' or 'severe bleeding', transfusion reactions or adverse events between pathogen-reduced and standard platelets. For a range of laboratory outcomes the results indicated evidence of some benefits for standard platelets over pathogen-reduced platelets. These conclusions are based on data from 1422 patients included in 10 trials. Results from ongoing or new trials are required to determine if there are clinically important differences in bleeding risk between pathogen-reduced platelet transfusions and standard platelet transfusions. Given the variability in trial design, bleeding assessment and quality of outcome reporting, it is recommended that future trials apply standardised approaches to outcome assessment and follow-up, including safety reporting.

Prophylactic platelet transfusion for prevention of bleeding in patients with haematological disorders after chemotherapy and stem cell transplantation

BACKGROUND

Platelet transfusions are used in modern clinical practice to prevent and treat bleeding in thrombocytopenic patients with bone marrow failure. Although considerable advances have been made in platelet transfusion therapy in the last 40 years, some areas continue to provoke debate especially concerning the use of prophylactic platelet transfusions for the prevention of thrombocytopenic bleeding.

OBJECTIVES

To determine the most effective use of platelet transfusion for the prevention of bleeding in patients with haematological disorders undergoing chemotherapy or stem cell transplantation.

SEARCH METHODS

This is an update of a Cochrane review first published in 2004. We searched for randomised controlled trials (RCTs) in the Cochrane Central Register of Controlled Trials (CENTRAL Issue 4, 2011), MEDLINE (1950 to Nov 2011), EMBASE (1980 to Nov 2011) and CINAHL (1982 to Nov 2011), using adaptations of the Cochrane RCT search filter, the UKBTS/SRI Transfusion Evidence Library, and ongoing trial databases to 10 November 2011.

SELECTION CRITERIA

RCTs involving transfusions of platelet concentrates, prepared either from individual units of whole blood or by apheresis, and given to prevent bleeding in patients with haematological disorders. Four different types of prophylactic platelet transfusion trial were included.

DATA COLLECTION AND ANALYSIS

In the original review one author initially screened all electronically derived citations and abstracts of papers, identified by the review search strategy, for relevancy. Two authors performed this task in the updated review. Two authors independently assessed the full text of all potentially relevant trials for eligibility. Two authors completed data extraction independently. We requested missing data from the original investigators as appropriate.

MAIN RESULTS

There were 18 trials that were eligible for inclusion, five of these were still ongoing.Thirteen completed published trials (2331 participants) were included for analysis in the review. The original review contained nine trials (718 participants). This updated review includes six new trials (1818 participants).Two trials (205 participants) in the original review are now excluded because fewer than 80% of participants had a haematological disorder.The four different types of prophylactic platelet transfusion trial, that were the focus of this review, were included within these thirteen trials.Three trials compared prophylactic platelet transfusions versus therapeutic-only platelet transfusions. There was no statistical difference between the number of participants with clinically significant bleeding in the therapeutic and prophylactic arms but the confidence interval was wide (RR 1.66; 95% CI 0.9 to 3.04).The time taken for a clinically significant bleed to occur was longer in the prophylactic platelet transfusion arm. There was a clear reduction in platelet transfusion usage in the therapeutic arm. There was no statistical difference between the number of participants in the therapeutic and prophylactic arms with platelet refractoriness, the only adverse event reported.Three trials compared different platelet count thresholds to trigger administration of prophylactic platelet transfusions. No statistical difference was seen in the number of participants with clinically significant bleeding (RR 1.35; 95% CI 0.95 to 1.9), however, this type of bleeding occurred on fewer days in the group of patients transfused at a higher platelet count threshold (RR 1.72; 95% CI 1.33 to 2.22).The lack of a difference seen for the number of participants with clinically significant bleeding may be due to the studies, in combination, having insufficient power to demonstrate a difference, or due to masking of the effect by a higher number of protocol violations in the groups of patients with a lower platelet count threshold. Using a lower platelet count threshold led to a significant reduction in the number of platelet transfusions used. There were no statistical differences in the number of adverse events reported between the two groups.Six trials compared different doses of prophylactic platelet transfusions. There was no evidence to suggest that using a lower platelet transfusion dose increased: the number of participants with clinically significant (WHO grade 2 or above) (RR 1.02; 95% CI 0.93 to 1.11), or life-threatening (WHO grade 4) bleeding (RR 1.87; 95% CI 0.86 to 4.08). A higher platelet transfusion dose led to a reduction in the number of platelet transfusion episodes, but an increase in total platelet utilisation. Only one adverse event, wheezing after transfusion, had a significantly higher incidence when standard and high dose transfusions were compared but this difference was not seen when low dose and high dose transfusions were compared. It is therefore likely to be a type I error (false positive).One small trial compared prophylactic platelet transfusions versus platelet-poor plasma. The risk of a significant bleed was decreased in the prophylactic platelet transfusion arm (RR 0.47; 95% CI 0.23 to 0.95) and this was statistically significant.All studies had threats to validity; the majority of these were due to methodology of the studies not being described in adequate detail.Although it was not the main focus of the review, it was interesting to note that in one of the pre-specified sub-group analyses (treatment type) two studies showed that patients receiving an autologous transplant have a lower risk of bleeding than patients receiving intensive chemotherapy or an allogeneic transplant (RR 0.73, 95% CI 0.65 to 0.82).

AUTHORS' CONCLUSIONS

These conclusions refer to the four different types of platelet transfusion trial separately. Firstly, there is no evidence that a prophylactic platelet transfusion policy prevents bleeding. Two large trials comparing a therapeutic versus prophylactic platelet transfusion strategy, that have not yet been published, should provide important new data on this comparison. Secondly, there is no evidence, at the moment, to suggest a change from the current practice of using a platelet count of 10 x 10(9)/L. However, the evidence for a platelet count threshold of 10 x 10(9)/L being equivalent to 20 x 10(9)/L is not as definitive as it would first appear and further research is required. Thirdly, platelet dose does not affect the number of patients with significant bleeding, but whether it affects number of days each patient bleeds for is as yet undetermined. There is no evidence that platelet dose affects the incidence of WHO grade 4 bleeding.Prophylactic platelet transfusions were more effective than platelet-poor plasma at preventing bleeding.

Therapeutic efficacy of platelet components treated with amotosalen and ultraviolet A pathogen inactivation method: results of a meta-analysis of randomized controlled trials

BACKGROUND AND OBJECTIVES

There are conflicting data regarding the therapeutic efficacy of platelets inactivated using amotosalen and ultraviolet A light. We have performed a meta-analysis to summarize the results of different randomized controlled trials (RCT).

MATERIALS AND METHODS

Five RCTs reported through March 2011 met the criteria for meta-analysis. Weighted mean difference (WMD) in corrected count increment (CCI) at 1 h, CCI-24 h, and transfusion interval (days) and summary odds ratio (OR) of bleeding in inactivated platelet (I-P) group vs. noninactivated platelet (C-P) group were calculated across studies.

RESULTS

Randomized controlled trials were statistically homogeneous when we analysed CCI-24 h, and the transfusion of C-P was associated with a higher CCI-24 h when compared with the transfusion of I-P (WMD, 3×10(3); 95% CI, 2·32×10(3)-3·69×10(3); P<0·00001). RCTs were statistically heterogeneous when we analysed CCI-1 h, transfusion interval and OR of bleeding. Regarding the OR of bleeding in the I-P and C-P groups, it varied by as much as a multiple of four among the trials, from 0·66 to 2·66. When we combined double-blinded and high methodologic quality score RCTs, the use of I-P was not statistically associated with an increase in the OR of bleeding when compared with the use of C-P (OR, 0·97; 95% CI, 0·75-1·27; P=0·84).

CONCLUSION

Although the transfusion of I-P was associated with lower CCI-24 h when compared with the transfusion of C-P, this was not associated with differences in the OR of bleeding between I-P and C-P.

Meta-analysis of the studies of bleeding complications of platelets pathogen-reduced with the Intercept system

BACKGROUND

The eligibility criteria of a previously reported meta-analysis (Transfusion 2011;51:1058-1071) of randomized controlled trials (RCTs) of pathogen reduction of platelets in patients with hypoproliferative thrombocytopenia were modified to examine the impact on the findings of: (1) inclusion of a (previously excluded) RCT; (2) restriction of eligibility to RCTs of the Intercept (amotosalen-HCl/ultraviolet-A-light) system; and (3) differences in the methods used to assess bleeding complications.

MATERIALS AND METHODS

Five RCTs comparing the risk of all, clinically significant (grades 2 through 4) and/or severe (grades 3 and 4) bleeding complications between recipients of platelets treated with Intercept vs. standard unmanipulated platelets were included. Odds ratios (ORs) of bleeding complications of similar severity recorded during similar periods of observation were calculated across all studies and across homogeneous subsets of studies by random-effects methods.

RESULTS

Treatment with Intercept increased all bleeding complications when four RCTs meeting the eligibility criteria of the previous meta-analysis were integrated, but not across all the five currently available studies [summary OR=1·24; 95% confidence interval (CI), 0·79-1·93]. Clinically significant bleeding complications increased when the results of the SPRINT RCT were based on the expanded safety analysis (summary OR=1·52; 95% CI, 1·09-2·12)--but not the initial report (summary OR=1·30; 95% CI, 0·54-3·14)--of that study.

CONCLUSIONS

Treatment with Intercept may increase the risk of all and clinically significant (albeit not severe) bleeding complications in RCTs maintaining a platelet count of ≥10×10(9) or ≥20×10(9)/l through increased platelet transfusions.

Pathogen-inactivation of platelet components with the INTERCEPT Blood System ™: a cohort study

INTRODUCTION

INTERCEPT treatment is used to reduce platelet transfusion associated bacterial infections. Limited data are available in Switzerland.

PATIENTS AND METHODS

Patients with thrombocytopenia or thrombocyte dysfunction requiring platelet transfusions were enrolled in a prospective cohort study on safety (primary endpoint) and efficacy (secondary endpoint) of INTERCEPT treated platelets (I-PLTs). I-PLTs were produced from double-dose apheresis products. Data on safety were actively recorded for each transfusion.

RESULTS

A total of 551 I-PLT units (mean platelet dose: 2.6 ± 0.4 × 10(11)/unit) were transfused to 46 patients (mean number of platelet transfusions per patient: 12 ± 12.5). Fifty-one (9%) transfusions were associated with adverse events and 12 (2%) with acute transfusion reactions. Eleven serious adverse events were observed, none considered as related to the administration of I-PLT. Mean 1-4h and 16-24h CCIs were 10.1 ± 8.1 and 3.6 ± 6.6, respectively.

CONCLUSION

The transfusion of I-PLT was associated with a good safety profile and adequate platelet count increments at 1-4h.

[Pathogen reduction for platelets: available techniques and recent developments]

The will to reach for blood components a microbiological safety comparable to that of plasma-derived drugs led to the development of numerous pathogen reduction research programs for red blood cells and\or platelets in the 1990s. A consensus conference organized in 2007 allowed to define the main steps and precautions to be taken for the implementation of these processes. In the specific case of platelet concentrates, three processes stay this day in the run, even if they are not at the same development stage. A process using ultraviolet C only is at the stage of preclinical studies. The Mirasol® process, based on the activation of riboflavin by exposure to ultraviolet A and ultraviolet B is CE marked (class IIb), and a clinical study was published in 2010. The Intercept® process, involving the activation of a psoralen molecule by exposure to ultraviolet A, is CE marked (class III) since 2002, and has been licensed in France since 2005, in Germany since 2005 and in Switzerland since 2010. At least 12 clinical studies have been published. In regard to this last pathogen reduction process, the medical and scientific documentation, from in vitro investigations to post-marketing observational studies, is much more developed than the corresponding documentation of some innovative processes at the time of their generalization, such as the SAG-mannitol solution for red cell concentrates in 1979, leukoreduction filters for platelets and red cells concentrates in the 1990s, the solvent detergent therapeutic plasma in 1992 or the methylene blue therapeutic plasma in 2006.

Methods for testing platelet function for transfusion medicine

BACKGROUND

Currently only indirect measures are required for monitoring the function of platelets in platelet concentrates (PC).

METHODS

This is an overview on currently available commercialized methods that have been used to determine platelet function in donors, concentrates and after transfusion. We show examples for the application of the no/low shear methods light-transmission aggregometry, flow cytometry, multiple electrode aggregometry, thrombelastography and dynamic light scattering, and those applying high shear, the platelet function analyzer-100, and the cone and plate analyzer. Advantages and disadvantages of the various methods to screen donors, evaluate the haemostatic properties maintained in the PC and after transfusion are discussed, based on considerations of platelet physiology, and the feasibility of the various procedures. This survey focuses on reports from the last 10 years, as the technology for the production of PCs has advanced significantly during the last few years.

CONCLUSION

Specific aspects of platelet function can be assessed by the no/low shear methods, while the high shear methods provide more general analysis of platelet haemostatic competence. Yet, there is no strong evidence that the in vitro data correspond with the clinical outcome.

In vitro and in vivo evaluation of apheresis platelets stored for 5 days in 65% platelet additive solution/35% plasma

BACKGROUND

In the United States, apheresis platelets (PLTs) are suspended in autologous plasma. PLT additive solutions, long used in Europe, decrease recipient allergic reactions and may reduce the risk of transfusion-related acute lung injury. We evaluated Amicus-collected PLTs stored in platelet additive solution (PAS) III (InterSol) for 5 days.

STUDY DESIGN AND METHODS

In Study 1, 71 subjects donated two products on a single day-one each stored in 100% plasma or 65% PAS III/35% plasma. Products underwent standard in vitro testing on Days 1 and 5. In Study 2, 43 additional subjects provided Amicus products stored for 5 days in 65% PAS III/35% plasma for in vivo radiolabeled recovery and survival determinations. The effect of approximately 2500cGy Day 1 gamma irradiation was evaluated in a subset of products.

RESULTS

PAS III PLTs (n=70) had a median Day 5 pH(22°C) of 7.2 (lower 95%, 95% tolerance limit, 6.9). Mean Day 5 recovery and survival of radiolabeled PAS III PLTs (n=33) were, respectively, 80.5 and 72.1%, of fresh autologous PLTs. With 95% confidence, these values were at least 66% of fresh PLT recovery and 58% of survival. All in vitro variables remained within ranges seen in licensed products for irradiated and nonirradiated PAS III PLTs.

CONCLUSION

Leukoreduced Amicus PLTs stored in 65% PAS III/35% plasma in PL-2410 containers maintained pH ≥6.9 throughout 5 days' storage. Radiolabeled PLT recovery and survival values met US Food and Drug Administration statistical criteria. Gamma-irradiated PAS III PLTs demonstrated no significant adverse effects due to irradiation in in vitro testing.

Meta-analysis of the randomized controlled trials of the hemostatic efficacy and capacity of pathogen-reduced platelets

BACKGROUND

A recent independently funded randomized controlled trial (RCT; Br J Haematol 2010;150:209-17) questioned prevailing opinion concerning the hemostatic capacity of pathogen-reduced platelets (PLTs). Meta-analysis was used to calculate the effect of pathogen reduction (PR) of PLTs on hemostatic efficacy and capacity based on all available data and to investigate possible reasons for the variation in reported findings.

STUDY DESIGN AND METHODS

RCTs allocating patients to receive routine PLT transfusions with pathogen-reduced or untreated PLTs and reporting on at least one of six hemostasis endpoints were eligible for analysis. Five RCTs of hemato-oncology patients met eligibility criteria. Endpoints determined by similar criteria in all RCTs were integrated by fixed-effects methods. Endpoints determined by different criteria were integrated by random-effects methods.

RESULTS

Studies were statistically homogeneous in all analyses. Pathogen-reduced PLTs were associated with a significant (p < 0.05) reduction in 1- and 24-hour posttransfusion corrected count increments (summary mean difference, 3260; 95% confidence interval [CI], 2450-4791; and summary mean difference, 3315; 95% CI, 2027-4603) as well as a significant increase in all and in clinically significant bleeding complications (summary odds ratio [OR], 1.58; 95% CI, 1.11-2.26; and summary OR, 1.54; 95% CI, 1.11-2.13). The frequency of severe bleeding complications did not differ.

CONCLUSION

The results of the recent RCT are not inconsistent with those of the earlier studies. Introduction of PR technologies in their current stage of development would result in an increase in mild and moderate (albeit not severe) bleeding complications, which the transfusion-medicine community must explicitly tolerate to reap the benefits from PR.

A systematic assessment of the quality of reporting for platelet transfusion studies

BACKGROUND

As evidence-based medicine assumes increasing importance, there is a need for high-quality reporting of clinical studies. A recent review of clinical platelet (PLT) studies indicated variability in reporting. We undertook a critical analysis of PLT transfusion studies to determine the quality of reporting.

STUDY DESIGN AND METHODS

A systematic MEDLINE search for clinical studies of PLT transfusion was performed to identify articles. Relevant observational studies (OBS) were critiqued using the STROBE checklist and randomized controlled clinical trials (RCTs) using the CONSORT checklist. Studies were further evaluated with a PLT-specific checklist developed by the authors. Observations were analyzed descriptively and using Pareto analysis.

RESULTS

A total of 772 articles were identified by the search. Eighty-six articles (23 RCTs and 63 OBS) met eligibility criteria. All RCTs, and a similar number of OBS (24), were randomly selected for analysis. Studies reported the scientific background and rationale, key results, and outcomes. OBS frequently did not consider bias and confounders. RCTs frequently did not explain bias, interim analyses, stopping rules, success of blinding, or weaknesses of multiple analyses. The PLT-specific critique found many studies adequately reported basics of the PLT product, PLT increment, and transfusion reactions. Studies frequently failed to report specific details of PLT compatibility, details of product preparation, and use of other blood products.

CONCLUSION

Recently published articles of clinical PLT transfusion share common strengths and weaknesses. The quality of reporting may be improved by providing guidelines to authors and journal editors that list the essential elements of a well-reported clinical study of PLT transfusion.

Pathogen inactivation/reduction of platelet concentrates: turning theory into practice

Background  Pathogen reduction technology (PRT) has been proven to reduce the residual risk of transmission of infectious agents. Reduction of various contaminating bacteriae, viruses and parasites by few to several log steps and efficiency to prevent GVHD has been shown. Aim  To evaluate and compare advantages and disadvantages of PRT available for practical application in platelets. Materials and Methods  PRT for the treatment of platelets is currently offered by two formats: Amotosalen (INTERCEPT, Cerus, Concord, CA, USA) and vitamin B2 (Mirasol, Caridian, Denver, USA). Results from different studies and our own experiences with the two techniques are compared and discussed. Results and Discussion  For both technologies, different groups of investigators have shown acceptable in-vitro results with respect to functional and storage data for platelets stored for up to 5 days after production and before transfusion. Initial clinical studies showed no inferiority of the treated platelets in comparison to untreated controls in thrombocytopenic patients. However for both techniques a tendency towards lower CCI has been reported, which may be more pronounced in the platelets treated with the Intercept process. For introduction of PRT many countries require not only CE mark but licensing with the respective authorities since treatment for pathogen reduction is regarded as creating a 'new' blood product. With respect to a platelet loss during pathogen reduction it seems recommendable to increase the lower limit of platelet content of the product to 2.5 × 1011. Particularly for the Intercept system, where a considerable amount of platelets is lost in the purification of the product from Amotosalen, a change in the production process to increase the platelet yield may be necessary. Data from our group show a tendency for improved functional and storage parameters for platelets treated with the Mirasol process. Compared to conventional manufacturing of platelets by apheresis or pooling of buffy coats, pathogen reduction requires additional labour, space, and quality control. Shelf life of platelets is limited in most countries because of the risk of bacterial contamination (in Germany presently to 4 days). A prolongation to 5 or more days after pathogen reduction seems feasible but remains a topic for future studies. Conclusion  Results of in vitro and clinical studies of pathogen reduced platelets are promising. Larger clinical trials will help to determine whether PRT proves to be beneficial (reduction of transmission of infections, less alloimmunisation) and overall cost effective (bearing in mind that additional costs may be compensated for by omission of gamma irradiation and potential longer shelf life).

Emerging infectious disease agents and their potential threat to transfusion safety

BACKGROUND

Emerging infections have been identified as a continuing threat to human health. Many such infections are known to be transmissible by blood transfusion, while others have properties indicating this potential. There has been no comprehensive review of such infectious agents and their threat to transfusion recipient safety to date.

STUDY DESIGN AND METHODS

The members of AABB's Transfusion Transmitted Diseases Committee reviewed a large number of information sources in order to identify infectious agents with actual or potential risk of transfusion transmission now or in the future in the US or Canada; with few exceptions, these agents do not have available interventions to reduce the risk of such transmission. Using a group discussion and writing process, key characteristics of each agent were identified, researched, recorded and documented in standardized format. A group process was used to prioritize each agent on the basis of scientific/epidemiologic data and a subjective assessment of public perception and/or concern expressed by regulatory agencies.

RESULTS

Sixty-eight infectious agents were identified and are described in detail in a single Supplement to TRANSFUSION. Key information will also be provided in web-based form and updated as necessary. The highest priorities were assigned to Babesia species, Dengue virus, and vCJD.

CONCLUSION

The information is expected to support the needs of clinicians and transfusion medicine experts in the recognition and management of emerging infections among blood donors and blood recipients.

Preparation, storage and quality control of platelet concentrates

Patients with thrombocytopaenia need transfusions of platelet concentrates to prevent or stop bleeding. A platelet transfusion should provide platelets with good functionality. The quality of platelet concentrates (PCs) is affected by the preparation method and the storage conditions including duration of storage, type of storage container, and storage solution (plasma or an additive solution). Different in vivo and in vitro techniques can be used to analyse PCs. Platelets can be collected by apheresis technique, and from whole blood using either the buffy-coat or the platelet-rich plasma method. PCs can be gamma irradiated to prevent occurrence of graft-versus-host disease in the recipient. Pathogen inactivation procedures have been developed to prevent transmission of bacteraemia.

Assessment of safety in neonates for transfusion of platelets and plasma prepared with amotosalen photochemical pathogen inactivation treatment by a 1-month intravenous toxicity study in neonatal rats

BACKGROUND

It is estimated that approximately 300,000 neonates undergo transfusions annually. The neonatal immune system is immature, making such patients more susceptible to the effects associated with transfusion-transmitted bacteria, viruses, protozoa, and white blood cells (WBCs). The INTERCEPT Blood System is a photochemical process (PCT) utilizing amotosalen and long-wavelength ultraviolet to inactivate pathogens and WBCs in both platelet (PLT) and plasma components for transfusion. A series of clinical studies has shown PCT PLTs and PCT plasma to be safe and effective for transfusion in adults and pediatric patients. Because clinical studies in neonates are technically difficult and ethically challenging, preclinical toxicologic studies were conducted in neonatal rats to evaluate the safety of PCT blood components for neonates.

STUDY DESIGN AND METHODS

This study examined daily intravenous administration to neonatal rats of amotosalen in 35 percent:65 percent plasma:InterSol from 1 microg per kg per day (representing 1-unit transfusion) to 457 microg per kg per day (representing multiple transfusions) from Postnatal Day 4 (PND4) to PND31. Rats were observed for viability, clinical signs, and body weights until PND31 and then subjected to pathology evaluation. Hematology, clinical chemistry, and urinalysis data were also collected on PND31. Toxicokinetic parameters were evaluated on PND4 and PND31.

RESULTS

There were no amotosalen-related effects on clinical signs, body weight, hematology, clinical chemistry, urinalysis, gross pathology, or histopathology, despite the exposure of neonatal rats to amotosalen concentrations as high as approximately 48 times the standard exposure in adult patients.

CONCLUSION

This study demonstrates the safety of PCT for transfusion in neonatal rats and augments data from other studies and clinical use supporting the use of PCT in neonatal patients.

A review of transfusion practice before, during, and after hematopoietic progenitor cell transplantation

The increased use of hematopoietic progenitor cell (HPC) transplantation has implications and consequences for transfusion services: not only in hospitals where HPC transplantations are performed, but also in hospitals that do not perform HPC transplantations but manage patients before or after transplantation. Candidates for HPC transplantation have specific and specialized transfusion requirements before, during, and after transplantation that are necessary to avert the adverse consequences of alloimmunization to human leukocyte antigens, immunohematologic consequences of ABO-mismatched transplantations, or immunosuppression. Decisions concerning blood transfusions during any of these times may compromise the outcome of an otherwise successful transplantation. Years after an HPC transplantation, and even during clinical remission, recipients may continue to be immunosuppressed and may have critically important, special transfusion requirements. Without a thorough understanding of these special requirements, provision of compatible blood components may be delayed and often urgent transfusion needs prohibit appropriate consultation with the patient's transplantation specialist. To optimize the relevance of issues and communication between clinical hematologists, transplantation physicians, and transfusion medicine physicians, the data and opinions presented in this review are organized by sequence of patient presentation, namely, before, during, and after transplantation.

Pathogen reduction: a precautionary principle paradigm

Although remarkable advances have been made in the prevention of the major transfusion-transmitted diseases, long intervals have transpired between the first recognition of transfusion risk and the implementation of a preventive strategy. For hepatitis B virus, that interval was 30 years; for non-A, non-B/hepatitis C virus, 15 years; and for human immunodeficiency virus, West Nile virus, Trypanosoma cruzi, and bacteria, 3, 4, 5, and 18 years, respectively. In our existing reactive approach, there is a fundamental and inevitable delay before we can react; and thus, infections are destined to occur. The continued emergence or reemergence of transfusion-transmitted infections calls for a new paradigm of preemptive pathogen reduction (PR). Two PR systems, psoralen/UV-A and riboflavin/UV-A, have shown efficacy and safety for platelets and plasma; and psoralen/UV-A technology has been successfully implemented for platelets in Europe. Pathogen reduction can eliminate or reduce the risk for any nucleic acid containing agent, including bacteria, and thus will be effective for all but prion diseases. It is possible to introduce PR for platelets and plasma now and to concentrate resources on developing PR for red cells. This will require an intellectual and financial commitment from the National Institutes of Health, the Food and Drug Administration, industry, and the blood bank establishment, just as occurred for nucleic acid testing (NAT) technology. This can be done if there is sufficient will to do it.

Proceedings of a Consensus Conference: pathogen inactivation-making decisions about new technologies

Significant progress has been made in reducing the risk of pathogen transmission to transfusion recipients. Nonetheless, there remains a continuing risk of transmission of viruses, bacteria, protozoa, and prions to recipients. These include many of the viruses for which specific screening tests exist as well as pathogens for which testing is currently not being done, including various species of bacteria, babesiosis, variant Creutzfeld-Jacob disease, hepatitis A virus, human herpes virus 8, chikungunya virus, Chagas disease, and malaria. Pathogen inactivation (PI) technologies potentially provide an additional way to protect the blood supply from emerging agents and also provide additional protection against both known and as-yet-unidentified agents. However, the impact of PI on product quality and recipient safety remains to be determined. The purpose of this consensus conference was to bring together international experts in an effort to consider the following issues with respect to PI: implementation criteria; licensing requirements; blood service and clinical issues; risk management issues; cost-benefit impact; and research requirements. These proceedings are provided to make available to the transfusion medicine community the considerable amount of important information presented at this consensus conference.

Nonsurgical bleeding diathesis in anemic thrombocytopenic patients: role of temperature, red blood cells, platelets, and plasma-clotting proteins

Research at the Naval Blood Research Laboratory (Boston, MA) for the past four decades has focused on the preservation of red blood cells (RBCs), platelets (PLTs), and plasma-clotting proteins to treat wounded servicemen suffering blood loss. We have studied the survival and function of fresh and preserved RBCs and PLTs and the function of fresh and frozen plasma-clotting proteins. This report summarizes our peer-reviewed publications on the effects of temperature, RBCs, PLTs, and plasma-clotting proteins on the bleeding time (BT) and nonsurgical blood loss. The term nonsurgical blood loss refers to generalized, systemic bleeding that is not corrected by surgical interventions. We observed that the BT correlated with the volume of shed blood collected at the BT site and to the nonsurgical blood loss in anemic thrombocytopenic patients after cardiopulmonary bypass surgery. Many factors influence the BT, including temperature; hematocrit (Hct); PLT count; PLT size; PLT function; and the plasma-clotting proteins factor (F)VIII, von Willebrand factor, and fibrinogen level. Our laboratory has studied temperature, Hct, PLT count, PLT size, and PLT function in studies performed in non-aspirin-treated and aspirin-treated volunteers, in aspirin-treated baboons, and in anemic thrombocytopenic patients. This monograph discusses the role of RBCs and PLTs in the restoration of hemostasis, in the hope that a better understanding of the hemostatic mechanism might improve the treatment of anemic thrombocytopenic patients. Data from our studies have demonstrated that it is important to transfuse anemic thrombocytopenic patients with RBCs that have satisfactory viability and function to achieve a Hct level of 35 vol percent before transfusing viable and functional PLTs. The Biomedical Excellence for Safer Transfusion (BEST) Collaborative recommends that preserved PLTs have an in vivo recovery of 66 percent of that of fresh PLTs and a life span that is at least 50 percent that of fresh PLTs. Their recommendation does not include any indication that preserved PLTs must be able to function to reduce the BT and reduce or prevent nonsurgical blood loss. One of the hemostatic effects of RBC is to scavenge endothelial cell nitric oxide, a vasodilating agent that inhibits PLT function. In addition, endothelin may be released from endothelial cells, a potent vasoconstrictor substance,to reduce blood flow at the BT site. RBCs, like PLTs at the BT site, may provide arachidonic acid and adenosine diphosphate to stimulate the PLTs to make thromboxane, another potent vasoconstrictor substance and a PLT-aggregating substance. At the BT site, the PLTs and RBCs are activated and phosphatidyl serine is exposed on both the PLTs and the RBCs. FVa and FXa, which generate prothrombinase activity to produce thrombin, accumulate on the PLTs and RBCs. A Hct level of 35 vol percent at the BT site minimizes shear stress and reduces nitric oxide produced by endothelial cells. The transfusion trigger for prophylactic PLT transfusion should consider both the Hct and the PLT count. The transfusion of RBCs that are both viable and functional to anemic thrombocytopenic patients may reduce the need for prophylactic leukoreduced PLTs, the alloimmunization of the patients, and the associated adverse events related to transfusion-related acute lung injury. The cost for RBC transfusions will be significantly less than the cost for the prophylactic PLT transfusions.