Effect of age of red cells for transfusion on patient outcomes: a systematic review and meta-analysis

Red blood cell transfusion in veno-arterial extracorporeal membrane oxygenation - the disconnect between oxygen delivery and tissue oxygenation

BackgroundRed cell transufion in veno-arterial membrane oxygenation (VA ECMO) has been widely debated.PurposeThis narrative review aims to examine the historical and current approaches of red cell transfusion in veno-arterial extracorporeal membrane oxygenation (VA ECMO) to enhance oxygen delivery. It will explore the potential benefits and pitfalls of red blood cell (RBC) transfusion in VA ECMO, including relationship between haemoglobin (Hb) concentration, tissue oxygenation and patient outcomes associated with transfusion. Following it will review the impact of cardiogenic shock on the microcirculation, performance of transfused RBC and effects of the ECMO circuit on RBC function. It will conclude with an introduction to potential mechanisms by which we might manipulate red cells to improve tissue oxygenation, without augmentation of Hb concentration.ConclusionFurther research is needed to provide insight into optimal RBC transfusion thresholds and strategies to augment red cell function to optimise tissue oxygenation in VA ECMO.

Innovations in red blood cell preservation

The global infrastructure supporting nearly 100 million transfusions annually relies on the ability to store red cell concentrates (RCCs) for up to 42 days at hypothermic temperatures or indefinitely at low sub-zero temperatures. While these methods are generally effective, there is both an opportunity and, in specific settings, a need to refine storage techniques that have remained largely unchanged since the 1980s. Recent research has identified ways to address limitations that were not fully understood when these methods were first implemented in blood banks, with much of it focusing on modifying conventional storage strategies, while some studies explore alternative approaches. In this review, we explore the current state of RBC preservation and the future prospects for advancing both short- and long-term storage strategies.

Improving RBC inventory by optimizing preoperative ordering and eliminating crossmatch and hold

BACKGROUND

Blood product constraints have increased the focus on inventory management as blood banks have faced challenges that impact supply chains and donor availability. Solutions often include a reduction in transfusion volumes through multidisciplinary improvements, but this is often coupled with a reduction in blood bank inventory to match reduced demand. We sought to improve inventory availability within the blood bank without modification of transfusion rates through solutions that prevented unnecessary RBC orders and crossmatching.

STUDY DESIGN AND METHODS

Improvements were focused on reduction of duplicate orders, preoperative blood orders, excess volume of blood orders, and crossmatching in advance of perioperative needs. The study monitored the improvement of the crossmatch to transfusion ratio as the primary outcome and days of shelf life until expiration as a secondary outcome.

RESULTS

The CT ratio of RBCs decreased from 2.03 (16,044/7922) pre-implementation to 1.67 (12,321/7375) post-implementation (p < 0.05). Our inventory was managed more efficiently following our interventions as demonstrated through the day of shelf life of RBCs issued. Pre-implementation, RBCs were issued an average of 17.5 days before expiration, which increased to 20.4 days post-implementation (p < 0.05).

CONCLUSION

Modification of preoperative order sets and education of clinical staff to ensure appropriate blood product ordering can significantly impact available inventory. Although this was also identified within our study, we found that the largest impact comes from a change in crossmatching workflow to reduce unnecessary reserving of RBCs. These changes can be implemented without significant impact to turnaround time.

Donor clinical characteristics and impacts on transfusion recipient outcomes

Clinical characteristics of blood donors may affect short- and long-term outcomes of transfusion recipients. The impact of donor sex and age on recipient outcomes have not yielded consistent results in observational studies. One recently published randomized controlled trial (iTADS) addressing the impact of donor sex on recipient outcomes noted no differences between a female versus male transfusion strategy; a second Canadian multicenter trial has just been funded. Other donor characteristics - including pregnancy history, smoking status, obesity, and chronic illnesses - remain incompletely explored. More robust clinical studies with vein-to-vein capabilities are needed to understand the complex interplay between donors and recipients.

The safety and efficacy of transfusing red blood cells stored for different durations: a systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

The aim of this work was to resolve the uncertainty of whether transfusion of fresher red blood cells (RBCs) is better or not with regard to the safety and efficacy.

METHODS

This systematic review was performed in accordance with our protocol registered on PROSPERO (https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022379183).

RESULTS

After a literature search, 13,247 records were identified, and 26 randomized controlled trials (RCTs) involving 53,859 participants were eligible and included in this review. The results in our review suggested that there was no significant effect of fresher vs older RBCs on mortality (relative risk [RR] = 1.04; 95% CI, 0.99-1.09; P = .39; I2 = 0%), transfusion reactions (RR = 0.87; 95% CI, 0.57-1.33; P = .64; I2 = 0%). However, the transfusion of fresher RBCs might increase the risk of nosocomial infection (RR = 1.11; 95% CI, 1.02-1.20; P = .02; I2 = 0%), whereas there was no significant difference in the fresh vs old subgroup (RR = 0.87; 95% CI, 0.68 to 1.12; P = .28; I2 = 0%).

CONCLUSION

Our study updated and reinforced the evidence of previously published systematic reviews that support the safety and efficiency of current practice of issuing the oldest available RBCs in the blood bank inventory.

Effect of storage duration on outcome of patients receiving red blood cell in emergency department

The effect of the duration of red blood cell (RBC) storage on the outcomes of transfused patients remains controversial, and studies on patients in the emergency department (ED) are limited. This study aimed to determine the association between RBC storage duration and outcomes of patients receiving transfusions in the ED. For RBCs issued to patients in the ED between 2017 and 2022, the storage period of the RBC and data on the transfused patient were obtained. Patients were divided into fresh (≤ 7 days) and old (> 7 days) RBC groups, and the associations between storage duration, outcomes, and laboratory changes were evaluated. There was no significant difference in outcomes between the two groups in the 28-day mortality (adjusted odds ratio [OR] 0.91, 95% confidence interval [CI] 0.75-1.10, P = 0.320) and the length of stay (fresh 13.5 ± 18.1 vs. old 13.3 ± 19.8, P = 0.814). Regarding changes in laboratory test results, the increase in hemoglobin and hematocrit levels was not affected by the storage durations. The study revealed that transfusion of older RBCs is not associated with inferior outcomes or adverse clinical consequences when compared to that of fresh RBCs in patients in the ED.

Effects of red blood cell transfusion on patients undergoing cardiac surgery in Queensland - a retrospective cohort study

BACKGROUND

Packed red blood cell (pRBC) transfusion is a relatively safe and mainstay treatment commonly used in cardiac surgical patients. However, there is limited evidence on clinical effects of transfusing blood nearing end-of shelf life that has undergone biochemical changes during storage.

OBJECTIVE

To investigate evidence of associations between morbidity/mortality and transfusion of blood near end of shelf-life (> 35 days) in cardiac surgical patients.

METHODS

Data from the Queensland Health Admitted Patient Data Collection database 2007-2013 was retrospectively analysed. Coronary artery bypass graft and valvular repair patients were included. Multivariable logistic regression was used to examine the effect of pRBC age (< 35 days vs. ≥ 35 days) on in-hospital mortality and morbidity. As secondary analysis, outcomes associated with the number of pRBC units transfused (≤ 4 units vs. ≥ 5 units) were also assessed.

RESULTS

A total of 4514 cardiac surgery patients received pRBC transfusion. Of these, 292 (6.5%) received pRBCs ≥ 35 days. No difference in in-hospital mortality or frequency of complications was observed. Transfusion of ≥ 5 units of pRBCs compared to the ≤ 4 units was associated with higher rates of in-hospital mortality (5.6% vs. 1.3%), acute renal failure (17.6% vs. 8%), infection (10% vs. 3.4%), and acute myocardial infarction (9.2% vs. 4.3%). Infection carried an odds ratio of 1.37 between groups (CI = 0.9-2.09; p = 0.14) and stroke/neurological complications, 1.59 (CI = 0.96-2.63; p = 0.07).

CONCLUSION

In cardiac surgery patients, transfusion of pRBCs closer to end of shelf-life was not shown to be associated with significantly increased mortality or morbidity. Dose-dependent differences in adverse outcomes (particularly where units transfused were > 4) were supported.

A randomized control trial to compare mortality in recipients of leucoreduced and non-leucoreduced whole blood transfusion in patients with cancer in Uganda

BACKGROUND

Mortality benefit of transfusion with leucoreduced whole blood has not been demonstrated in the sub-Saharan Africa (SSA). We compared mortality in patients with cancer transfused with leucoreduced and non-leucoreduced whole blood in a SSA setting.

METHODS

An open-label randomized controlled trial was conducted at the Uganda Cancer Institute where participants were randomized in a 1:1 ratio into the leucoreduced and non-leucoreduced whole blood transfusion arms. Leucocyte filtration of whole blood was performed within 72 h of blood collection. Patients aged ≥ 15 years who were prescribed blood transfusion by the primary physicians were eligible for study enrolment. Mortality difference was analyzed using intention-to-treat survival analysis and cox proportional hazard model was used to analyze factors associated with mortality.

RESULTS

There were 137 participants randomized to the leucoreduced and 140 to the non-leucoreduced arms. Baseline characteristics were similar between the two arms. The median number of blood transfusions received was 1 (IQR, 1-3) unit and 2 (IQR, 1-3) units in the leucoreduced and non-leucoreduced arms respectively, p = 0.07. The 30-day mortality rate in the leucoreduced arm was 4.6% (95% CI, 2.1-10) and was 6.2% (95% CI, 3.2-12.1) in the non-leucoreduced arm (p = 0.57), representing an absolute effect size of only 1.6%. Increasing age (HR = 0.92, 95% CI, 0.86-0.98, p = 0.02) and Eastern Co-operative Oncology Group (ECOG) performance score of 1 (HR = 0.03, 95% CI, 0.00-0.31, p < 0.01) were associated with reduced 30-day mortality.

CONCLUSIONS

The study failed to demonstrate mortality difference between cancer patients transfused with leucoreduced and non-leucoreduced whole blood. Although this study does not support nor refute universal leucoreduction to reduce mortality in patients with cancer in SSA, it demonstrates the feasibility of doing transfusion RCTs in Uganda, where a multi-center trial with an appropriate sample size is needed.

TRIAL REGISTRATION

Pan African Clinical Trial Registry, https://pactr.samrc.ac.za/ (PACTR202302787440132). Registered on 06/02/2023.

Estimated median density identifies donor age and sex differences in red blood cell biological age

BACKGROUND

Donors possess heterogeneous red cell concentrates (RCCs) in terms of the biological age of their red blood cells (RBCs) as a direct result of various donor-dependent factors influencing rates of erythropoiesis. This study aimed to estimate the median biological age of RBCs in RCCs based on donor age and sex to investigate inherent differences in blood products' biological ages over hypothermic storage using estimated median densities (EMDs).

STUDY DESIGN

Sixty RCCs were collected from four donor groups; male and female teenagers (17-19 years old) and seniors (75+ years old). A Percoll density-based separation approach was used to quantify the EMDs indicative of biological age. EMD and mean corpuscular hemoglobin (MCHC) were compared by correlation analyses.

RESULTS

Differences in the median biological age of RCC units were observed with male donors having significantly higher EMDs compared to females (p < .001). Teen male donors possessed the highest EMDs with significantly elevated levels of biologically aged RBCs compared to both female donor groups, regardless of storage duration (p < .05). Throughout most of the 42-day storage period, senior donors, particularly senior females, demonstrated the strongest correlation between EMD and MCHC (R2 > 0.5).

CONCLUSIONS

This study provides further evidence that there are inherent differences between the biological age profiles of RBCs between blood donors of different sex and age. Our findings further highlight that biological age may contribute to RBC quality during storage and that donor characteristics need to be considered when evaluating transfusion safety and efficacy.

Donor pregnancies and transfusion recipient mortality: A role for red blood cell storage?

BACKGROUND AND OBJECTIVES

Donor characteristics have been implicated in transfusion-related adverse events. Uncertainty remains about whether sex, and specifically pregnancy history of the blood donor, could affect patient outcomes. Whether storage duration of the blood product could be important for patient outcomes has also been investigated, and a small detrimental effect of fresh products remains a possibility. Here, we hypothesize that fresh red blood cell products donated by ever-pregnant donors are associated with mortality in male patients.

MATERIALS AND METHODS

We used data from a cohort study of adult patients receiving a first transfusion between 2005 and 2015 in the Netherlands. The risk of death after receiving a transfusion from one of five exposure categories (female never-pregnant stored ≤10 days, female never-pregnant stored >10 days, female ever-pregnant stored ≤10 days, female ever-pregnant stored >10 days and male stored for ≤10 days), compared to receiving a unit donated by a male donor, which was stored for >10 days (reference), was calculated using a Cox proportional hazards model.

RESULTS

The study included 42,456 patients who contributed 88,538 person-years in total, of whom 13,948 died during the follow-up of the study (33%). Fresh units (stored for ≤10 days) from ever-pregnant donors were associated with mortality in male patients, but the association was not statistically significant (hazard ratio 1.39, 95% confidence interval 0.97-1.99). Sensitivity analyses did not corroborate this finding.

CONCLUSION

These findings do not consistently support the notion that the observed association between ever-pregnant donor units and mortality is mediated by blood product storage.

Exploring the potential harm of varied blood storage on patients undergoing cardiovascular surgery

BACKGROUND AND OBJECTIVES

Debate exists surrounding the optimal duration of red blood cell (RBC) storage. A hypothesis emerging from previous research suggests that exposure to fresh blood may be harmful to patients undergoing cardiac surgery. This study uses a large transfusion medicine database to explore the association between in-hospital mortality and red cell storage duration.

MATERIALS AND METHODS

This is an exploratory retrospective cohort study of all adult patients at Hamilton, Canada, over a 14-year period that received at least one allogeneic red cell transfusion during their hospitalization for cardiac surgery requiring bypass. The primary outcome for the study was in-hospital death. Analysis was performed using multivariate Cox regression modelling with time-dependent and time-independent covariates and stratification variables. Five models with varying definitions for short, intermediate and prolonged duration of RBC storage were tested.

RESULTS

From March 2004 to December 2017, 11,205 patients met the inclusion criteria and were included in the regression analyses. No significant effect of short-duration red storage on patient mortality was observed in all statistical models, with the red cells stored for the longest duration as the reference group. When patients who received exclusively fresh (hazard ratio [HR] 1.040, 95% confidence interval [CI] 0.588-1.841, p-value = 0.893) and older aged (HR 1.038, 95% CI 0.769-1.1.402, p-value = 0.0801) RBCs were compared with those who received exclusively mid-age red cells as the reference, statistical significance was similarly not reached.

CONCLUSION

Red cells stored for the shortest duration are not associated with increased risk of mortality among cardiac surgery patients.

Transfused Red Blood Cell Characteristics and Kidney Transplant Outcomes Among Patients Receiving Early Posttransplant Transfusion

Importance

Red blood cell transfusion (RBCT) is frequently required in the early post-kidney transplant period, but long-term outcomes associated with RBCT is controversial. Therefore, it may be relevant to investigate the association between RBCT characteristics and transplant outcomes.

Objective

To study the association between RBC storage duration and transplant outcomes.

Design, Setting, and Participants

This was a nationwide retrospective cohort study based on data linking between 2 prospective French nationwide registries. Clinical transplant parameters, outcomes, and RBCT characteristics were extracted from the CRISTAL registry of the Agence de la Biomédecine and the national database of the Etablissement Français du Sang. All 12 559 patients having received a first kidney transplant in France between January 1, 2002, and December 31, 2008, were included. Patients were followed up from transplant to graft loss, death with a functional graft, or data retrieval in June 2016. Data were analyzed from April 2019 to June 2022.

Exposures

Clinical outcomes of transplant recipients who underwent early RBCT were analyzed considering transfusion characteristics.

Main Outcomes and Measures

Cox proportional hazards regression models were fitted to evaluate transplant failure defined as graft loss or death with a functional graft.

Results

Among 12 559 patients who underwent kidney transplant, 3483 received an RBCT during the first 14 days posttransplant. The median (IQR) age of patients was 53.0 (41.5-61.2) years, and 1929 patients (55.4%) were male. Median (IQR) follow-up was 7.8 (7.6-8.0) years. In multivariable analysis, longer (vs shorter) storage duration of transfused RBC was associated with a decrease in risk of transplant failure (hazard ratio, 0.99; 95% CI, 0.98-1.00 for each additional storage day; P = .06). Patients transfused with at least 1 RBC unit stored for more than 20 days had a 5% absolute decrease in transplant failure at 3 years and 7% at 5 years compared with those who received RBC stored for less than 20 days.

Conclusions and Relevance

In this study, longer RBC storage duration was associated with a decreased risk of transplant failure among patients who received kidney transplants and RBC transfusions. Preferential use of RBC with longer storage duration might improve kidney graft survival following transplant and transfusion.

Red Blood Cell Transfusions Are Not Associated With Incident Complications or Poor Outcomes in Patients With Intracerebral Hemorrhage

Background Anemia is associated with poor intracerebral hemorrhage (ICH) outcomes, yet the relationship of red blood cell (RBC) transfusions to ICH complications and functional outcomes remains unclear. We investigated the impact of RBC transfusion on hospital thromboembolic and infectious complications and outcomes in patients with ICH. Methods and Results Consecutive patients with spontaneous ICH enrolled in a single-center, prospective cohort study from 2009 to 2018 were assessed. Primary analyses assessed relationships of RBC transfusions on incident thromboembolic and infectious complications occurring after the transfusion. Secondary analyses assessed relationships of RBC transfusions with mortality and poor discharge modified Rankin Scale score 4 to 6. Multivariable logistic regression models adjusted for baseline demographics and medical disease severity (Acute Physiology and Chronic Health Evaluation II), and ICH severity (ICH score).Of 587 patients with ICH analyzed, 88 (15%) received at least one RBC transfusion. Patients receiving RBC transfusions had worse medical and ICH severity. Though patients receiving RBC transfusions had more complications at any point during the hospitalization (64.8% versus 35.9%), we found no association between RBC transfusion and incident complications in our regression models (adjusted odds ratio [aOR], 0.71 [95% CI, 0.42-1.20]). After adjusting for disease severity and other relevant covariates, we found no significant association between RBC transfusion and mortality (aOR, 0.87 [95% CI, 0.45-1.66]) or poor discharge modified Rankin Scale score (aOR, 2.45 [95% CI, 0.80-7.61]). Conclusions In our cohort with ICH, RBC transfusions were expectedly given to patients with higher medical and ICH severity. Taking disease severity and timing of transfusions into account, RBC transfusion was not associated with incident hospital complications or poor clinical ICH outcomes.

Intervening on the Storage Time of RBC Units and its Effects on Adverse Recipient Outcomes using Real-World Data

Emulating hypothetical randomized trials using large real-world data may be well suited to address the issues of prior RBC transfusion RCTs.

Our study suggests that transfusing RBC units stored for >1 or 2 weeks increases recipient mortality.

Randomized controlled trials (RCTs) have found no evidence that the storage time of transfused red blood cell (RBC) units affects recipient survival. However, inherent difficulties in conducting RBC transfusion RCTs have prompted critique of their design, analyses, and interpretation. Here, we address these issues by emulating hypothetical randomized trials using large real-world data to further clarify the adverse effects of storage time. We estimated the comparative effect of transfusing exclusively older vs fresher RBC units on the primary outcome of death, and the secondary composite end point of thromboembolic events, or death, using inverse probability weighting. Thresholds were defined as 1, 2, 3, and 4 weeks of storage. A large Danish blood transfusion database from the period 2008 to 2018 comprising >900 000 transfusion events defined the observational data. A total of 89 799 patients receiving >340 000 RBC transfusions during 28 days of follow-up met the eligibility criteria. Treatment with RBC units exclusively fresher than 1, 2, 3, and 4 weeks of storage was found to decrease the 28-day recipient mortality with 2.44 percentage points (pp) (0.86 pp, 4.02 pp), 1.93 pp (0.85 pp, 3.02 pp), 1.06 pp (–0.20 pp, 2.33 pp), and −0.26 pp (–1.78 pp, 1.25 pp) compared with transfusing exclusively older RBC units, respectively. The 28-day risk differences for the composite end point were similar. This study suggests that transfusing exclusively older RBC units stored for >1 or 2 weeks increases the 28-day recipient mortality and risk of thromboembolism or death compared with transfusing fresher RBC units.

Storage-Induced Micro-Erythrocytes Can Be Quantified and Sorted by Flow Cytometry

Refrigerated storage of red cell concentrates before transfusion is associated with progressive alterations of red blood cells (RBC). Small RBC (type III echinocytes, sphero-echinocytes, and spherocytes) defined as storage-induced micro-erythrocytes (SME) appear during pretransfusion storage. SME accumulate with variable intensity from donor to donor, are cleared rapidly after transfusion, and their proportion correlates with transfusion recovery. They can be rapidly and objectively quantified using imaging flow cytometry (IFC). Quantifying SME using flow cytometry would further facilitate a physiologically relevant quality control of red cell concentrates. RBC stored in blood bank conditions were stained with a carboxyfluorescein succinimidyl ester (CFSE) dye and incubated at 37°C. CFSE intensity was assessed by flow cytometry and RBC morphology evaluated by IFC. We observed the accumulation of a CFSE ^high RBC subpopulation by flow cytometry that accounted for 3.3 and 47.2% at day 3 and 42 of storage, respectively. IFC brightfield images showed that this CFSE ^high subpopulation mostly contains SME while the CFSE ^low subpopulation mostly contains type I and II echinocytes and discocytes. Similar numbers of SME were quantified by IFC (based on projected surface area) and by flow cytometry (based on CFSE intensity). IFC and scanning electron microscopy showed that ≥95% pure subpopulations of CFSE ^high and CFSE ^low RBC were obtained by flow cytometry-based sorting. SME can now be quantified using a common fluorescent dye and a standard flow cytometer. The staining protocol enables specific sorting of SME, a useful tool to further characterize this RBC subpopulation targeted for premature clearance after transfusion.

Modelling haemoglobin incremental loss on chronic red blood cell transfusions

BACKGROUND AND OBJECTIVES

Understanding the impact of red blood cell (RBC) lifespan, initial RBC removal, and transfusion intervals on patient haemoglobin (Hb) levels and total iron exposure is not accessible for chronic transfusion scenarios. This article introduces the first model to help clinicians optimize chronic transfusion intervals to minimize transfusion frequency.

MATERIALS AND METHODS

Hb levels and iron exposure from multiple transfusions were calculated from Weibull residual lifespan distributions, the fraction effete RBC removed within 24-h (X_e ) and the nominal Hb increment. Two-unit transfusions of RBCs initiated at patient [Hb] = 7 g/dl were modelled for different RBC lifespans and transfusion intervals from 18 to 90 days, and X_e from 0.1 to 0.5.

RESULTS

Increased X_e requires shorter transfusion intervals to achieve steady-state [Hb] of 9 g/dl as follows: 30 days between transfusions at X_e  = 0.5, 36 days at X_e  = 0.4, 42 days at X_e  = 0.3, 48 days at X_e  = 0.2 and 54 days at X_e  = 0.1. The same transfusion interval/X_e pairs result in a steady-state [Hb] = 8 g/dl when the RBC lifespan was halved. By reducing transfused RBC increment loss from 30% to 10%, annual transfusions were decreased by 22% with iron addition decreased by 24%. Acute dosing of iron occurs at the higher values of X_e on the day after a transfusion event.

CONCLUSION

Systematic trends in fractional Hb incremental loss X_e have been modelled and have a significant and calculatable impact on transfusion intervals and associated introduction of iron.

Transfusion-Associated Delirium in Children: No Difference Between Short Storage Versus Standard Issue RBCs

OBJECTIVES

Primary objective is to determine if transfusion of short storage RBCs compared with standard issue RBCs reduced risk of delirium/coma in critically ill children. Secondary objective is to assess if RBC transfusion was independently associated with delirium/coma.

DESIGN

This study was performed in two stages. First, we compared patients receiving either short storage or standard RBCs in a multi-institutional prospective randomized controlled trial. Then, we compared all transfused patients in the randomized controlled trial with a single-center cohort of nontransfused patients matched for confounders of delirium/coma.

SETTING

Twenty academic PICUs who participated in the Age of Transfused Blood in Critically Ill Children trial.

PATIENTS

Children 3 days to 16 years old who were transfused RBCs within the first 7 days of admission.

INTERVENTIONS

Subjects were randomized to either short storage RBC study arm (defined as RBCs stored for up to seven days) or standard issue RBC study arm. In addition, subjects were screened for delirium prior to transfusion and every 12 hours after transfusion for up to 3 days.

MEASUREMENTS AND MAIN RESULTS

Primary outcome measure was development of delirium/coma within 3 days of initial transfusion. Additional outcome measures were dose-response relationship between volume of RBCs transfused and delirium/coma, and comparison of delirium/coma rates between transfused patients and individually matched nontransfused patients. We included 146 subjects in the stage I analysis; 69 were randomized to short storage RBCs and 77 to standard issue. There was no significant difference in delirium/coma development between study arms (79.5% vs 70.1%; p = 0.184). In the stage II analysis, adjusted odds for delirium in the transfused cohort was more than eight-fold higher than in the nontransfused matched cohort, even after controlling for hemoglobin (adjusted odds ratio, 8.9; CI, 2.8-28.4; p < 0.001).

CONCLUSIONS

RBC transfusions (and not anemia) are independently associated with increased odds of subsequent delirium/coma. However, storage age of RBCs does not affect delirium risk.

Association between perioperative allogeneic red blood cell transfusion and infection after clean-contaminated surgery: a retrospective cohort study

BACKGROUND

Allogeneic red blood cell (RBC) transfusion can induce immunosuppression, which can then increase the susceptibility to postoperative infection. However, studies in different types of surgery show conflicting results regarding this effect.

METHODS

In this retrospective cohort study conducted in a tertiary referral centre, we included adult patients undergoing clean-contaminated surgery from 2014 to 2018. Patients who received allogeneic RBC transfusion from preoperative Day 30 to postoperative Day 30 were included into the transfusion group. The control group was matched for the type of surgery in a 1:1 ratio. The primary outcome was infection within 30 days after surgery, which was defined by healthcare-associated infection, and identified mainly based on antibiotic regimens, microbiology tests, and medical notes.

RESULTS

Among the 8098 included patients, 1525 (18.8%) developed 1904 episodes of postoperative infection. Perioperative RBC transfusion was associated with an increased risk of postoperative infection after controlling for 27 confounders by multivariable regression analysis (odds ratio [OR]: 1.60; 95% confidence interval [CI]: 1.39-1.84; P<0.001) and propensity score weighing (OR: 1.64; 95% CI: 1.45-1.85; P<0.001) and matching (OR: 1.70; 95% CI: 1.43-2.01; P<0.001), and a dose-response relationship was observed. The transfusion group also showed higher risks of surgical site infection, pneumonia, bloodstream infection, multiple infections, intensive care admission, unplanned reoperation, prolonged postoperative length of hospital stay, and all-cause death.

CONCLUSIONS

Perioperative allogeneic RBC transfusion is associated with an increased risk of infection after clean-contaminated surgery in a dose-response manner. Close monitoring of infections and enhanced prophylactic strategies should be considered after transfusion.

Age of red blood cells is not associated with in-hospital mortality in massively transfused patients

BACKGROUND

Studies comparing mortality following massive transfusion (MT) with fresher versus longer-stored red blood cells (RBCs) have focused on trauma patients. The Australian and New Zealand Massive Transfusion Registry collects data on all adult MT cases (≥5 RBCs within 4 hours, any bleeding context, ≥18 years) at participating hospitals.

METHODS

Years 2007 to 2018 data from 29 hospitals were analyzed to quantify the association between mortality and RBC storage time in adult MT cases. We ran three logistic regression models separately on each of seven bleeding contexts, with in-hospital mortality as the outcome and, in turn, (1) mean storage time (STmean) quartiles, (2) proportion of RBCs ≥30 days old (propOLD), and (3) scalar age of blood index as predictors.

RESULTS

A total of 8,685 adult MT cases involving transfusion of 126,622 RBCs were analyzed with Australian and New Zealand data analyzed separately. Mean storage times for these cases were (by quartile in ascending order) as follows: Australia, 12.5 days (range, 3.1-15.5 days), 17.7 (15.5-19.9), 22.3 (19.9-24.9), and 29.8 (24.9-41.7); New Zealand, 11.3 days (3.6-13.7), 15.3 (13.7-16.8), 18.7 (16.8-20.7), and 24.5 (20.7-35.6). The odds ratios comparing in-hospital mortality for each quartile with that of the control first quartile (freshest blood), proportion of longer-stored (≥30 days) RBCs, and scalar age of blood index were not statistically significant across all bleeding contexts.

CONCLUSION

We find no correlation between in-hospital mortality and storage time of transfused RBCs in a large cohort of adult MT patients representing all bleeding contexts. These results are consistent with those of recent large multicenter trials.

LEVEL OF EVIDENCE

Epidemiologic, level III; Therapeutic, level IV.

Rapid clearance of storage-induced microerythrocytes alters transfusion recovery

Permanent availability of red blood cells (RBCs) for transfusion depends on refrigerated storage, during which morphologically altered RBCs accumulate. Among these, a subpopulation of small RBCs, comprising type III echinocytes, spheroechinocytes, and spherocytes and defined as storage-induced microerythrocytes (SMEs), could be rapidly cleared from circulation posttransfusion. We quantified the proportion of SMEs in RBC concentrates from healthy human volunteers and assessed correlation with transfusion recovery, investigated the fate of SMEs upon perfusion through human spleen ex vivo, and explored where and how SMEs are cleared in a mouse model of blood storage and transfusion. In healthy human volunteers, high proportion of SMEs in long-stored RBC concentrates correlated with poor transfusion recovery. When perfused through human spleen, 15% and 61% of long-stored RBCs and SMEs were cleared in 70 minutes, respectively. High initial proportion of SMEs also correlated with high retention of RBCs by perfused human spleen. In the mouse model, SMEs accumulated during storage. Transfusion of long-stored RBCs resulted in reduced posttransfusion recovery, mostly due to SME clearance. After transfusion in mice, long-stored RBCs accumulated predominantly in spleen and were ingested mainly by splenic and hepatic macrophages. In macrophage-depleted mice, splenic accumulation and SME clearance were delayed, and transfusion recovery was improved. In healthy hosts, SMEs were cleared predominantly by macrophages in spleen and liver. When this well-demarcated subpopulation of altered RBCs was abundant in RBC concentrates, transfusion recovery was diminished. SME quantification has the potential to improve blood product quality assessment. This trial was registered at www.clinicaltrials.gov as #NCT02889133.

Higher donor body mass index is associated with increased hemolysis of red blood cells at 42-days of storage: A retrospective analysis of routine quality control data

BACKGROUND

For reasons unclear, some stored red blood cells (RBCs) have low hemolysis, while others have high hemolysis, which impacts quality consistency. To identify variables that influence hemolysis, routine quality control (QC) data for 42-days-stored RBCs with corresponding donor information were analyzed.

STUDY DESIGN AND METHODS

RBC QC and donor data were obtained from a national blood supplier. Regression models and analyses were performed on total cohort stratified by donor sex and by high hemolysis (≥90th percentile) vs control (<90th percentile) samples, including matching.

RESULTS

Data included 1734 leukoreduced RBCs (822 female, 912 male), processed by buffy coat-poor or whole blood filtration methods. Male RBCs had larger volume, hemoglobin content, and higher hemolysis than female RBCs (median hemolysis, 0.24% vs 0.21%; all P < .0001). Multivariable regression identified increased body mass index (BMI) and RBC variables were associated with higher hemolysis (P < .0001), along with older female age and buffy coat-poor processing method (P < .002). Logistic regression models comparing the high and control hemolysis subsets, matched for RBC component variables and processing method, identified overweight-obese BMI (>27 kg/m² ) in males remained the single donor-related variable associated with higher hemolysis (P < .0001); odds ratio, 3 (95% confidence interval [CI], 1.3-6.7), increasing to 4 (95% CI, 1.8-8.6) for obese males (BMI > 30 kg/m² ). Female donor obesity and older age trended toward higher hemolysis.

CONCLUSION

Donor BMI, sex, and female age influence the level of hemolysis of 42-days-stored RBCs. Other factors, not identified in this study, also influence the level of hemolysis.

Inter-donor variability in deformability of red blood cells in blood units

OBJECTIVE

This study aimed to examine the donor-to-donor variability in the deformability of red blood cells (RBCs) from freshly collected blood donations (F-RBC) and packed RBCs.

BACKGROUND

Packed RBCs are supplied for transfusion by the first-in-first-out (FIFO) criterion, assuming that their quality is the same for packed RBCs with equal storage duration. To challenge this notion, we determined the deformability of F-RBC and packed RBCs stored for different durations.

METHODS

Three RBC groups were employed: A. 79 samples of F-RBC; B. 76 samples of packed RBC units, randomly used for transfusion at different storage durations; and C. 65 samples of outdated packed RBCs stored for 35 to 37 days. All packed RBC units were non-leukofiltrated and stored in Citrate-phosphate-dextrose solution with adenine (CPDA-1). RBC deformability was determined using a computerised cell-flow properties analyser, which monitors the shape change of cells directly visualised in a narrow-gap flow chamber and provides the cells' deformability distribution in a large RBC population.

RESULTS

The F-RBC deformability exhibited a wide-range inter-donor variability. The cold storage of packed RBCs exerted a mild reduction of deformability, which became significant, compared to the initial inter-donor variability, only after 3 weeks of storage.

CONCLUSION

Packed RBCs are generally supplied for transfusion by the FIFO criterion based on the assumption that the storage duration is a key factor of RBC quality. This study demonstrates that the deformability of red blood cells is significantly different in donors, and substantial variability persists throughout the entire process of their storage. Therefore, the FIFO criterion is not sufficient for assessing the RBC deformability, which should, therefore, be specifically characterised for each unit.

Red Blood Cells and Hemoglobin in Human Atherosclerosis and Related Arterial Diseases

As the main particulate component of the circulating blood, RBCs play major roles in physiological hemodynamics and impact all arterial wall pathologies. RBCs are the main determinant of blood viscosity, defining the frictional forces exerted by the blood on the arterial wall. This function is used in phylogeny and ontogeny of the cardiovascular (CV) system, allowing the acquisition of vasomotricity adapted to local metabolic demands, and systemic arterial pressure after birth. In pathology, RBCs collide with the arterial wall, inducing both local retention of their membranous lipids and local hemolysis, releasing heme-Fe⁺⁺ with a high toxicity for arterial cells: endothelial and smooth muscle cells (SMCs) cardiomyocytes, neurons, etc. Specifically, overloading of cells by Fe⁺⁺ promotes cell death. This local hemolysis is an event associated with early and advanced stages of human atherosclerosis. Similarly, the permanent renewal of mural RBC clotting is the major support of oxidation in abdominal aortic aneurysm. In parallel, calcifications promote intramural hemorrhages, and hemorrhages promote an osteoblastic phenotypic shift of arterial wall cells. Different plasma or tissue systems are able, at least in part, to limit this injury by acting at the different levels of this system.

Management and prevention of anemia (acute bleeding excluded) in adult critical care patients

OBJECTIVE

Anemia is very common in critical care patients, on admission (affecting about two thirds of patients), but also during and after their stay, due to repeated blood loss, the effects of inflammation on erythropoiesis, a decreased red blood cell life span, and haemodilution. Anemia is associated with severity of illness and length of stay.

METHODS

A committee composed of 16 experts from four scientific societies, SFAR, SRLF, SFTS and SFVTT, evaluated three fields: (1) anaemia prevention, (2) transfusion strategies and (3) non-transfusion treatment of anaemia. Population, Intervention, Comparison, and Outcome (PICO) questions were reviewed and updated as needed, and evidence profiles were generated. Analysis of the literature and formulation of recommendations were then conducted according to the GRADE® methodology.

RESULTS

The SFAR-SRLF guideline panel provided ten statements concerning the management of anemia in adult critical care patients. Acute haemorrhage and chronic anemia were excluded from the scope of these recommendations. After two rounds of discussion and various amendments, a strong consensus was reached for ten recommendations. Three of these recommendations had a high level of evidence (GRADE 1±) and four had a low level of evidence (GRADE 2±). No GRADE recommendation could be provided for two questions in the absence of strong consensus.

CONCLUSIONS

The experts reached a substantial consensus for several strong recommendations for optimal patient management. The experts recommended phlebotomy reduction strategies, restrictive red blood cell transfusion and a single-unit transfusion policy, the use of red blood cells regardless of storage time, treatment of anemic patients with erythropoietin, especially after trauma, in the absence of contraindications and avoidance of iron therapy (except in the context of erythropoietin therapy).

Management and prevention of anemia (acute bleeding excluded) in adult critical care patients

Objective

Anemia is very common in critical care patients, on admission (affecting about two-thirds of patients), but also during and after their stay, due to repeated blood loss, the effects of inflammation on erythropoiesis, a decreased red blood cell life span, and haemodilution. Anemia is associated with severity of illness and length of stay.

Methods

A committee composed of 16 experts from four scientific societies, SFAR, SRLF, SFTS and SFVTT, evaluated three fields: (1) anemia prevention, (2) transfusion strategies and (3) non-transfusion treatment of anemia. Population, Intervention, Comparison, and Outcome (PICO) questions were reviewed and updated as needed, and evidence profiles were generated. Analysis of the literature and formulation of recommendations were then conducted according to the GRADE^® methodology.

Results

The SFAR–SRLF guideline panel provided ten statements concerning the management of anemia in adult critical care patients. Acute haemorrhage and chronic anemia were excluded from the scope of these recommendations. After two rounds of discussion and various amendments, a strong consensus was reached for ten recommendations. Three of these recommendations had a high level of evidence (GRADE 1±) and four had a low level of evidence (GRADE 2±). No GRADE recommendation could be provided for two questions in the absence of strong consensus.

Conclusions

The experts reached a substantial consensus for several strong recommendations for optimal patient management. The experts recommended phlebotomy reduction strategies, restrictive red blood cell transfusion and a single-unit transfusion policy, the use of red blood cells regardless of storage time, treatment of anaemic patients with erythropoietin, especially after trauma, in the absence of contraindications and avoidance of iron therapy (except in the context of erythropoietin therapy).

Effect of Fresh vs Standard-issue Red Blood Cell Transfusions on Multiple Organ Dysfunction Syndrome in Critically Ill Pediatric Patients: A Randomized Clinical Trial

IMPORTANCE

The clinical consequences of red blood cell storage age for critically ill pediatric patients have not been examined in a large, randomized clinical trial.

OBJECTIVE

To determine if the transfusion of fresh red blood cells (stored ≤7 days) reduced new or progressive multiple organ dysfunction syndrome compared with the use of standard-issue red blood cells in critically ill children.

DESIGN, SETTING, AND PARTICIPANTS

The Age of Transfused Blood in Critically-Ill Children trial was an international, multicenter, blinded, randomized clinical trial, performed between February 2014 and November 2018 in 50 tertiary care centers. Pediatric patients between the ages of 3 days and 16 years were eligible if the first red blood cell transfusion was administered within 7 days of intensive care unit admission. A total of 15 568 patients were screened, and 13 308 were excluded.

INTERVENTIONS

Patients were randomized to receive either fresh or standard-issue red blood cells. A total of 1538 patients were randomized with 768 patients in the fresh red blood cell group and 770 in the standard-issue group.

MAIN OUTCOMES AND MEASURES

The primary outcome measure was new or progressive multiple organ dysfunction syndrome, measured for 28 days or to discharge or death.

RESULTS

Among 1538 patients who were randomized, 1461 patients (95%) were included in the primary analysis (median age, 1.8 years; 47.3% girls), in which there were 728 patients randomized to the fresh red blood cell group and 733 to the standard-issue group. The median storage duration was 5 days (interquartile range [IQR], 4-6 days) in the fresh group vs 18 days (IQR, 12-25 days) in the standard-issue group (P < .001). There were no significant differences in new or progressive multiple organ dysfunction syndrome between fresh (147 of 728 [20.2%]) and standard-issue red blood cell groups (133 of 732 [18.2%]), with an unadjusted absolute risk difference of 2.0% (95% CI, -2.0% to 6.1%; P = .33). The prevalence of sepsis was 25.8% (160 of 619) in the fresh group and 25.3% (154 of 608) in the standard-issue group. The prevalence of acute respiratory distress syndrome was 6.6% (41 of 619) in the fresh group and 4.8% (29 of 608) in the standard-issue group. Intensive care unit mortality was 4.5% (33 of 728) in the fresh group vs 3.5 % (26 of 732) in the standard-issue group (P = .34).

CONCLUSIONS AND RELEVANCE

Among critically ill pediatric patients, the use of fresh red blood cells did not reduce the incidence of new or progressive multiple organ dysfunction syndrome (including mortality) compared with standard-issue red blood cells.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01977547.

Impact of red blood cell transfusion dose density on progression-free survival in patients with lower-risk myelodysplastic syndromes

Progression-free survival (PFS) of patients with lower-risk myelodysplastic syndromes (MDS) treated with red blood cell transfusions is usually reduced, but it is unclear whether transfusion dose density is an independent prognostic factor. The European MDS Registry collects prospective data at 6-monthly intervals from newly diagnosed lower-risk myelodysplastic syndromes patients in 16 European countries and Israel. Data on the transfusion dose density - the cumulative dose received at the end of each interval divided by the time since the beginning of the interval in which the first transfusion was received - were analyzed using proportional hazards regression with time-varying co-variates, with death and progression to higher-risk MDS/acute myeloid leukemia as events. Of the 1,267 patients included in the analyses, 317 died without progression; in 162 patients the disease had progressed. PFS was significantly associated with age, EQ-5D index, baseline World Health Organization classification, bone marrow blast count, cytogenetic risk category, number of cytopenias, and country. Transfusion dose density was inversely associated with PFS (P<1×10⁻⁴): dose density had an increasing effect on hazard until a dose density of 3 units/16 weeks. The transfusion dose density effect continued to increase beyond 8 units/16 weeks after correction for the impact of treatment with erythropoiesis-stimulating agents, lenalidomide and/or iron chelators. In conclusion, the negative effect of transfusion treatment on PFS already occurs at transfusion densities below 3 units/16 weeks. This indicates that transfusion dependency, even at relatively low dose densities, may be considered as an indicator of inferior PFS. This trial was registered at www.clinicaltrials.gov as #NCT00600860.

Haematological quality and age of donor blood issued for paediatric transfusion to four hospitals in sub-Saharan Africa

BACKGROUND AND OBJECTIVES

Paediatric blood transfusion for severe anaemia in hospitals in sub-Saharan Africa remains common. Yet, reports describing the haematological quality of donor blood or storage duration in routine practice are very limited. Both factors are likely to affect transfusion outcomes.

MATERIALS AND METHODS

We undertook three audits examining the distribution of pack types, haematological quality and storage duration of donor blood used in a paediatric clinical trial of blood at four hospitals in Africa (Uganda and Malawi).

RESULTS

The overall distribution of whole blood, packed cells (plasma-reduced by centrifugation) and red cell concentrates (RCC) (plasma-reduced by gravity-dependent sedimentation) used in a randomised trial was 40·7% (N = 1215), 22·4% (N = 669) and 36·8% (N = 1099), respectively. The first audit found similar median haematocrits of 57·0% (50·0,74·0), 64·0% (52·0,72·5; P = 0·238 vs. whole blood) and 56·0% (48·0,67·0; P = 0·462) in whole blood, RCC and packed cells, respectively, which resulted from unclear pack labelling by blood transfusion services (BTS). Re-training of the BTS, hospital blood banks and clinical teams led to, in subsequent audits, significant differences in median haematocrit and haemoglobins across the three pack types and values within expected ranges. Median storage duration time was 12 days (IQR: 6, 19) with 18·2% (537/2964) over 21 days in storage. Initially, 9 (2·8%) packs were issued past the recommended duration of storage, dropping to 0·3% (N = 7) in the third audit post-training.

CONCLUSION

The study highlights the importance of close interactions and education between BTS and clinical services and the importance of haemovigilance to ensure safe transfusion practice.

Does Transfusion of Blood and Blood Products Increase the Length of Stay in Hospital?

We aimed to analyze the use of blood products in cardiac surgery and to investigate its effect on clinical outcomes. Perioperative transfusion requirement, survival and complication rates and the duration of hospitalization were noted. Patients were divided into two groups considering the duration of hospital and intensive care unit (ICU) stay. The cardiopulmonary bypass time and the cross clamp time, and the amount of used cryoprecipitate, fresh frozen plasma, platelet, red blood cell and the bleeding amount were significantly higher in groups that stayed at the hospital for > 7 days and at the ICU for > 2 days (p > 0.05). In the univariate model, to predict the patients who might stay at the hospital for more than 1 week and who might stay at the ICU for more than 3 days, we considered the significant efficacy of postoperative blood transfusion, bleeding amount, and the cardiopulmonary bypass time (p < 0.05). In the reduced multivariate model, however, we analyzed the significant-independent efficacy of the postoperative fresh frozen plasma use to determine the patients who would stay at the hospital for more than 1 week and who would stay at the ICU for more than 3 days (p < 0.05). We have concluded that increased use of blood products was associated with the cross clamp and cardiopulmonary bypass time and prolonged duration of hospital and ICU stays. In open cardiac surgeries, the use of blood products due to bleeding was identified as a predictor for staying longer than 3 days at the ICU and longer than 7 days at the hospital.

The contribution of red blood cell transfusion to neonatal morbidity and mortality

Anaemia of prematurity will affect 90% of all very preterm infants, resulting in at least one red blood cell (RBC) transfusion. A significant proportion of preterm infants require multiple transfusions over the course of hospital admission. Growing evidence supports an association between transfusion exposure and adverse neonatal outcomes. In adults, transfusion-associated sepsis, transfusion-related acute lung injury and haemolytic reactions are the leading causes of transfusion-related morbidity and mortality; however, these are seldom recognised in newborns. The association between transfusion and adverse outcomes remains inconclusive. However, the evidence from preclinical studies demonstrates that RBC products can directly modulate immune cell function, a pathway termed transfusion-related immunomodulation (TRIM), which may provide a mechanism linking transfusion exposure with neonatal morbidities. Finally, we discuss the impact of TRIM on transfusion medicine, how we may address these issues and the emerging areas of research aimed at improving the safety of transfusions in this vulnerable population.

Resuscitation Fluid Choices to Preserve the Endothelial Glycocalyx

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2019. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2019. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Impact of different standard red blood cell storage temperatures on human and canine RBC hemolysis and chromium survival

BACKGROUND

Storage temperature is a critical factor for maintaining red-blood cell (RBC) viability, especially during prolonged cold storage. The target range of 1 to 6°C was established decades ago and may no longer be optimal for current blood-banking practices.

STUDY DESIGN AND METHODS

Human and canine RBCs were collected under standard conditions and stored in precision-controlled refrigerators at 2°C, 4°C, or 6°C.

RESULTS

During 42-day storage, human and canine RBCs showed progressive increases in supernatant non-transferrin-bound iron, cell-free hemoglobin, base deficit, and lactate levels that were overall greater at 6°C and 4°C than at 2°C. Animals transfused with 7-day-old RBCs had similar plasma cell-free hemoglobin and non-transferrin-bound iron levels at 1 to 72 hours for all three temperature conditions by chromium-51 recovery analysis. However, animals transfused with 35-day-old RBCs stored at higher temperatures developed plasma elevations in non-transferrin-bound iron and cell-free hemoglobin at 24 and 72 hours. Despite apparent impaired 35-day storage at 4°C and 6°C compared to 2°C, posttransfusion chromium-51 recovery at 24 hours was superior at higher temperatures. This finding was confounded by a preparation artifact related to an interaction between temperature and storage duration that leads to removal of fragile cells with repeated washing of the radiolabeled RBC test sample and renders the test sample unrepresentative of the stored unit.

CONCLUSIONS

RBCs stored at the lower bounds of the temperature range are less metabolically active and produce less anaerobic acidosis and hemolysis, leading to a more suitable transfusion product. The higher refrigeration temperatures are not optimal during extended RBC storage and may confound chromium viability studies.

The age of blood in pediatric intensive care units (ABC PICU): study protocol for a randomized controlled trial

Background

The “Age of Blood in Children in Pediatric Intensive Care Unit” (ABC PICU) study is a randomized controlled trial (RCT) that aims to determine if red blood cell (RBC) unit storage age affects outcomes in critically ill children. While RBCs can be stored for up to 42 days in additive solutions, their efficacy and safety after long-term storage have been challenged. Preclinical and clinical observational evidence suggests loss of efficacy and lack of safety of older RBC units, especially in more vulnerable populations such as critically ill children. Because there is a belief that shorter storage will improve outcomes, some physicians and institutions systematically transfuse fresh RBCs to children. Conversely, the standard practice of blood banks is to deliver the oldest available RBC unit (first-in, first-out policy) in order to decrease wastage.

Methods/design

The ABC PICU study, is a double-blind superiority trial comparing the development of “New or Progressive Multiple Organ Dysfunction Syndrome” (NPMODS) in 1538 critically ill children randomized to either transfusion with RBCs stored for ≤ 7 days or to standard-issue RBCs (oldest in inventory). Patients are being recruited from 52 centers in the US, Canada, France, Italy, and Israel.

Discussion

The ABC PICU study should have significant implications for blood procurement services. A relative risk reduction of 33% is postulated in the short-storage arm. If a difference is found, this will indicate that fresher RBCs do improve outcomes in the pediatric intensive care unit population and would justify that use in critically ill children.

If no difference is found, this will reassure clinicians and transfusion medicine specialists regarding the safety of the current system of allocating the oldest RBC unit in inventory and will discourage clinicians from preferentially requesting fresher blood for critically ill children.

Trial registration

ClinicalTrials.gov, ID: NCT01977547. Registered on 6 November 2013.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-2809-y) contains supplementary material, which is available to authorized users.