A simple method for obtaining platelet concentrates free of aggregates

Effect of bedside filtration on aggregates from cold-stored whole blood-derived platelet-rich plasma and apheresis platelet concentrates

BACKGROUND

The current approach to manufacture cold-stored platelets (CSP) replicates that of room temperature-stored platelets (RSP). However, this production method is associated with aggregate formation in CSP, a major pitfall that leads to significant wastage. We hypothesized that isolating platelets from whole blood as platelet-rich plasma (PRP) and storing them at a lower concentration reduces aggregates and that conventional bedside transfusion filtration removes CSP aggregates.

METHODS

We collected platelets from healthy humans by apheresis (AP) and by phlebotomy, from which we generated platelet-rich plasma (PRP). We split each AP and PRP platelets into two equal aliquots, storing one at 22°C (RT-PRP and RT-AP) and the other at 4°C (4C-PRP and 4C-AP). We evaluated platelets on day 0 and day 7 of storage. After storage, we measured platelet counts, aggregates, and other key characteristics before and after filtration by a bedside filter.

RESULTS

After storage, the 4C-AP platelet counts decreased significantly. 4C-PRP preserved glucose better and prevented a significant increase in lactate contrary to 4C-AP. Filtration led to significantly lower platelet counts in both 4C-PRP and 4C-AP but not in their RT counterparts. Post filtration, we observed 50% fewer aggregates only in 4C-AP, whereas 4C-PRP showed an unexpected but significant increase in aggregates. Testing confirmed activation during storage but filtration did not further activate platelets.

CONCLUSION

We provide evidence that 4C-PRP is an alternative to 4C-AP and that bedside filters reduce aggregates from 4C-AP. Further studies are needed to evaluate the hemostatic potential of 4C-PRP and the management of aggregates.

Blood platelet kinetics and platelet transfusion

The discovery of citrate anticoagulant in the 1920s and the development of plastic packs for blood collection in the 1960s laid the groundwork for platelet transfusion therapy on a scale not previously possible. A major limitation, however, was the finding that platelet concentrates prepared from blood anticoagulated with citrate were unsuitable for transfusion because of platelet clumping. We found that this could be prevented by simply reducing the pH of platelet-rich plasma to about 6.5 prior to centrifugation. We used this approach to characterize platelet kinetics and sites of platelet sequestration in normal and pathologic states and to define the influence of variables such as anticoagulant and ABO incompatibility on post-transfusion platelet recovery. The "acidification" approach enabled much wider use of platelet transfusion therapy until alternative means of producing concentrates suitable for transfusion became available.

Current status of additive solutions for platelets

The storage of platelets in additive solution (PAS) had lagged behind red cell concentrates, especially in North America. The partial or complete removal of anticoagulated plasma and storage of platelet concentrates in AS presents many advantages. The PAS can be formulated to optimize aerobic metabolism or decrease platelet activation, thus abrogating the platelet storage lesion and potentially improving in vivo viability. Plasma removal has been shown to reduce allergic reactions and the plasma harvested could contribute to the available plasma pool for transfusion or fractionation. PAS coupled to pathogen reduction technology results in a platelet product of equivalent hemostatic efficacy to conventionally stored platelets. Given the above, the likely future direction of platelet storage will be in new generation designer PAS with an extended shelf life and a superior safety profile to plasma stored platelets. J. Clin. Apheresis, 2012. © 2012 Wiley Periodicals, Inc.

Use of random versus apheresis platelet concentrates

The respective use of random (RPC) and apheresis (APC) platelet concentrates is highly heterogeneous among countries, ranging from 10 to 98% RPC in countries supposed to provide a similar transfusion service to patients. Moreover, when considering each country in the past 10 years, one can observe that some have changed their policy, switching from a majority of APC to RPC or vice versa. This presentation intends to analyse which factors may impact such decisions. For many years, the only available platelet component was a RPC obtained from whole blood donation by a two centrifugation steps process, the "platelet rich plasma" or PRP method. Since the beginning of the 1970s, APCs became available, with in fact many different techniques leading to many APCs that may not be equivalent. Since the end of the 1980s, a new method of RPC preparation was developed, using the buffy-coat (BC-PC), providing a blood component with highly preserved platelet functions as compared to RPCs prepared by the PRP technique. Finally, the use of each of these components either native, or leuco-reduced, or suspended in a storage solution, or processed with a pathogen inactivation technique adds new layers of complexity to compare them. Innumerable references can be found in the literature describing in vitro functional parameters of platelet concentrates. Although it is clear that BC-RPC retain much more their in vitro functions than PRP-RPC, indicating that no one should use the latter any more, it is much more difficult to distinguish differences between other PCs. Conversely, only a very few studies have been published related to a comparison of clinical efficacy of RPC versus APC, the endpoints being mainly CCI. Similarly to the in vitro studies, although RPC prepared with the PRP method show the lowest CCIs, no clear difference exists between "modern" RPC and APC. Another factor that may impact policy decision is the occurrence of adverse reactions in recipients. When considering only comparable data, for example leuco-reduced RPC versus leuco-reduced APC, there is now evidence that the latter is more associated with adverse reactions in recipients: data from hemovigilance in France show that, although no difference is noted for febrile non haemolytic transfusion reactions, nor for bacteria contamination, the incidence of allergic adverse reactions is about four times higher with APC as compared with RPC. Other aspects may impact the decision: the fact that using APC in place of RPC reduces the total donor exposure of patients was considered critical in some countries to reduce the risk of transmission of blood transmissible disease. Finally, the cost of the components, much higher for APC may be considered.

A critical comparison of platelet preparation methods

PURPOSE OF REVIEW

Platelet concentrates may be prepared from whole blood or by plateletpheresis. Currently, the non-evidence-based preponderance of apheresis units in the United States and the 50: 50 ratio in Europe may not optimize the gifts of whole-blood donors or minimize healthcare costs. Post-storage pooled, whole-blood-derived platelets, on the other hand, do not provide the convenience of or an equivalent level of safety as apheresis platelets.

RECENT FINDINGS

Some data suggest that different methods of manufacture of whole-blood-derived platelets (platelet-rich plasma or buffy coat intermediate steps) result in differing degrees of platelet activation, which may impact on the quality of stored concentrates. Recent studies have observed superior radiolabel recovery and post-transfusion increments for platelets derived from apheresis compared with platelet-rich plasma whole-blood-derived platelets. A pre-storage pooling system for whole-blood-derived platelets has just been licensed in the USA, and may eventually combine the benefits of apheresis-derived and whole-blood-derived platelets. The advantages of the European method of manufacture of buffy coat whole-blood-derived platelet concentrate have convinced the Canadian Blood Services to abandon platelet-rich-plasma-derived concentrates.

SUMMARY

We present a literature-based review of the relative merits of apheresis-derived and whole-blood-derived platelets. Additional studies are needed in order to define the optimal proportion of the platelet supply from apheresis collections and the choice of whole-blood-derived production method for US blood providers.

Reevaluation of the resting time period when preparing whole blood-derived platelet concentrates with the platelet-rich plasma method

BACKGROUND

The resting of platelet (PLT) pellets during the preparation of whole blood-derived PLT concentrates (PCs) is considered an essential step. A reevaluation of the rest period was conducted because preparation and storage conditions have been modified during the past 20 years.

STUDY DESIGN AND METHODS

A two-site in vitro study (Study 1) was conducted with rest times of 0 to 5 minutes, 1 hour, and 4 hours (n = 31-33 per rest period). Leukoreduced PCs were stored for 5 days. A second study (Study 2) measuring in vivo viability was conducted at a third site (14 paired studies). PCs were prepared from 2 units of whole blood on the same day to simultaneously compare viability following storage and radioisotopic labeling.

RESULTS

In Study 1, comparable in vitro parameters and swirling were observed with the three rest periods. The mean (+/-1 SD) values after storage for the extent of shape change and hypotonic stress parameters were 0 to 5 minutes, 16.7 +/- 7.2 and 66.0 +/- 15.7%; 1 hour, 19.1 +/- 6.9 and 69.3 +/- 17.9%; and 4 hours, 17.6 +/- 5.5 and 64.1 +/- 11.3%. In Study 2, the in vivo recovery was 49.9 +/- 15.3 and 50.9 +/- 20.2% with 0- to 5-minute and 1-hour rest periods, respectively. The corresponding survival time was 111.2 +/- 50.7 and 114.9 +/- 43.8 hours.

CONCLUSION

These studies indicate comparable in vitro and in vivo viability properties with 0- to 5-minute and 1-hour rest periods and at 4 hours (in vitro only).

Circulation and distribution of 111-In-oxine-labeled autologous baboon platelet aggregates and buffy coat

BACKGROUND

Although it is known that RBC concentrates may contain buffy coat and platelet concentrates may contain platelet aggregates, the circulation and distribution of these materials in the blood products have never been reported.

STUDY DESIGN AND METHODS

Baboon platelets were labeled with 111-In-oxine, aggregated with ADP and autotransfused without a filter. Baboon buffy coat was stored at 4 degrees C, labeled with 111-In-oxine and autotransfused without a filter. The circulation of the radiolabeled platelets and buffy coat was measured and the distribution of the buffy coat and platelet aggregates was measured by external scanning of the baboon using a gamma camera. The effects of the infusion of aggregated platelets, buffy coat, and gelatin on the plasma fibronectin level also were evaluated.

RESULTS

The 111-In-oxine labeled platelet aggregates were initially sequestered in the lungs and released into the peripheral blood during the next 3h, during which time the cell associated radioactivity increased by about 25%. Following the autotransfusion of 111-In-oxine labeled buffy coat, the 111-In-oxine radioactivity over the lungs increased, but decreased during the 60-min post-transfusion period as the radioactivity over the liver increased. Cell-associated radioactivity increased by about 10% over the 3-h post-transfusion period. Fibronectin levels decreased by 3% following the autotransfusion of platelet aggregates, by 10% after the autotransfusion of buffy coat and by 50% after the infusion of gelatin.

CONCLUSIONS

111-In-oxine radioactivity in the platelet aggregates and buffy coat was initially sequestered in the lungs, and 10-25% of the 111-In-oxine cell-associated radioactivity was released into the circulation during the 24-h post-transfusion period.

Use of hollow fiber membrane filtration for the removal of DMSO from platelet concentrates

It has been hypothesized that, in addition to freezing injury, some damage to platelets may result from the cell packing that occurs during removal of the cryoprotectant. This study examined DMSO removal by fluid exchange across hollow-fiber (HF) filters as an alternative to centrifugation. The DMSO solution with or without cell suspension was passed once through the filter. The optimum exchange during unloading of DMSO was determined by varying the flow rates in the external and internal compartments of the HF filter. Initially, buffered solutions of a 5% DMSO solution in the absence of platelets were pumped into the fibers and exchanged against PBS. The residual DMSO was determined by osmometry. The exchange of DMSO across the membrane was flow dependent and also influenced by the chemical nature of the HF fibers. No protocol using a reasonable rate flow through the fibers removed more than 95% of the DMSO in a single pass. The optimum protocol was achieved with polysynthane fibers with an internal flow rate of approximately 20 mi/min and an external flow rate of 100 ml/min. Subsequently, frozen/thawed platelet concentrates in DMSO were washed using centrifugation and compared to the HF filtration method. Platelet quality was assayed by flow cytometry, cell count, morphology and osmotic stress test. Both filtration and centrifugal washing techniques resulted in comparable morphological scores and numbers of discoid cells. When agents reducing platelet activation were added, platelet quality was improved after washing by either technique. The lower platelet osmotic response with HF filtration than with centrifugation while using activation inhibitors was attributed to the remaining amount of the inhibitors. All other parameters tested were similar. The expression of CD62P was equivalent with both techniques, and centrifugation did not activate platelets more than filtration contrary to what was originally anticipated. In conclusion, platelet quality was comparable after washing by either technique but hollow fiber filtration does remove cryoprotectant more rapidly than does centrifugation.

Storage of buffy coat preparations at 22 degrees C in plastic containers with different gas permeability

BACKGROUND

Buffy coats (BCs) are used as an alternative to platelet-rich plasma in the preparation of platelet concentrates (PCs). For this purpose the BCs have to be stored for same time at 20-24 degrees C which implies cellular metabolic activity. However, little information is available concerning the effects of a number of factors which may influence the suitability of the preparation as the source of PC.

STUDY DESIGN AND METHODS

We studied the effects on BCs of a high and low gas permeability of the wall of the plastic containers, PL2209 and PL146, respectively, mixing versus non-mixing during storage for 48 h at 22 degrees C, and two types of anticoagulant solutions, CPD and half strength citrate CPD (0.5CPD). The buffy coats were prepared by the bottom and top technique. The median values of volume and haematrocrit were 58-64 ml and 39-45%, respectively. A total of 48 BCs were tested. Blood gases, pH, bicarbonate concentration and haemolysis were determined in the blood mixtures and beta-thromboglobulin (beta-TG), lactate dehydrogenase (LDH), complement factor 3a, and elastase in the extracellular fluid.

RESULTS

The pH decreased in all units but to a lesser extent in PL2209 containers than in PL146 units. In the former the pCO2 decreased slowly in contrast to the latter where it increased by about 50%. Mixing during storage increased the pH and decreased the pCO2 in 0.5CPD-PL146 and CPD-PL2209 units, as compared to resting, while no effects of mixing were observed in the other groups. The pO2 decreased to low levels in PL146 units. The haemolysis and LDH release were higher in mixed than in unmixed units. The initial beta-TG levels were lowest in 0.5CPD-PL146 units which also had the lowest 24-hour levels. The release of beta-TG during storage was smallest in CPD resting units. The elastase release was significantly higher in 0.5CPD than in CPD units already from the beginning of storage and increased during storage at about the same rate irrespective of mixing. The C3a levels were higher in 0.5CPD-PL2209 units than in the other units at 2 h. Storage for 24 h caused an increase by 2-3 times of the original level without any clear relation to storage conditions.

CONCLUSIONS

In BC units accumulation of CO2 occurs in containers with low gas permeability. These also show the most rapid pH decrease during storage. Prolonged holding of BCs puts extra emphasis on the need of satisfactory gas permeability of the container for platelet storage in BC-derived PCs. Continuous mixing causes red cell damage and does not seem to have any clear benefit. The release of granulocyte elastase was higher in 0.5CPD than in CPD units but there was no indication of an associated increase in platelet activation.

SUMMARY

Study of buffy coats stored in various media and containers at 22 degrees C suggests that it is better to restrict storage to 24 h or less to avoid activation or other deleterious effects on the platelets.

Comparative efficacy of liposomes containing synthetic bacterial cell wall analogues for tumoricidal activation of monocytes and macrophages

We examined the activation to the tumoricidal state of normal mouse peritoneal exudate macrophages, bone marrow macrophages, and human blood monocytes by liposomes containing either lipophilic muramyl tripeptide (CGP 19,835) or a new synthetic analogue of lipoprotein from gram-negative bacteria outer wall, CGP 31,362, or combinations of the two. The superiority of liposomes containing the synthetic lipopeptide over liposomes containing lipophilic muramyl tripeptide for in vitro activation of monocytes and macrophages was demonstrated in several experiments. First, liposome-CGP-19,835 activated monocytes only in the presence of interferon-gamma, whereas activation with liposome-CGP 31,362 was interferon-independent. Second, activation of both mouse macrophages and human blood monocytes by liposome-CGP 31,362 occurred at a lower liposomal concentration than that by liposome-CGP 19,835. Third, monocytes incubated with liposome-CGP 31,362 released both tumor necrosis factor (TNF) and interleukin-1 activities, whereas monocytes treated with liposome-CGP 19,835 (in the absence of interferon-gamma) released only TNF activity. These data suggest that liposomes containing the synthetic lipopeptide CGP 31,362 are superior to liposomes containing CGP 19,835 for systemic activation of macrophages.

The preparation of platelet concentrates by the light-spin/hard-spin technique

For at least two decades the light-spin/hard-spin (LS/HS) method for preparation of platelet concentrates (PC) has been the standard of platelet support. With concern over the detrimental effects of platelet activation during component preparation and with increased recognition of the adverse consequences resulting from residual donor leukocytes in PC, new approaches to the production of PC have begun. This review addresses two aspects of the traditional LS/HS method of platelet preparation: platelet activation and residual leukocyte content. Studies of platelet activation are reviewed which focus on the second (hard-spin) centrifugation step during which pelleting of platelets occurs. Platelets studied immediately after the hard-spin exhibit evidence of alpha-granule release, expression of activation antigens, and decreased aggregation. There is a suggestion that some degree of reversal of platelet activation routinely occurs during the rest period following the hard-spin. The residual leukocyte content of PC prepared by the LS/HS method ranges from 10 7 to 10 9 leukocytes/unit. The residual donor leukocytes are predominantly lymphocytes and monocytes. Degeneration of residual donor leukocytes may release soluble cytokines resulting in febrile transfusion reactions. It remains controversial whether or not the cell-membrane fragments and microvesicles of degenerating donor leukocytes are capable of HLA allosensitization or viral transmission. Release of leukocyte elastase from degenerating leukocytes during platelet storage has been proposed as contributing to the platelet storage lesion. More research is needed to address the question of whether or not pre-storage leukocyte reduction during component preparation will result in improved PC. It appears likely that within the next few years radical changes will occur in the method of preparation of PC with the aim of providing the greatest degree of hemostatic effectiveness with the least toxicity to patients.

Cryopreservation of human platelets and bone marrow and peripheral blood totipotential mononuclear stem cells

Human platelets in sufficient numbers for a therapeutic transfusion can be collected for preservation either by pooling ABO- and Rh-compatible platelets or by apheresis procedures using mechanical cell-separating machines. Human platelets have been frozen successfully with 5 or 6% dimethyl sulfoxide (DMSO) and stored at -150 or -180 degrees C, respectively. Platelets frozen with 5% DMSO have been stored at -150 degrees C for at least 3 years, and platelets frozen with 6% DMSO have been stored at -80 degrees C for at least 2 years. Approximately 95% of the DMSO usually is removed by washing the platelets after thawing, and the residual DMSO produces no untoward effects. Washed platelets resuspended in plasma can be stored at room temperature for 6 to 8 hr before transfusion. Platelets thus frozen have freeze-thaw-wash recovery values of about 80%. In vivo survival values are only about 50% those seen with fresh platelets, and it is necessary to transfuse twice as many to achieve comparable results. Studies have shown that these platelets have satisfactory circulation, reduce clinical bleeding, and shorten the prolonged bleeding times associated with thrombocytopenia. Studies are now being made on human bone marrow and peripheral blood, from which totipotential cells devoid of immunocompetent cells can be isolated and frozen.

Effect of new plastics and leucocyte contamination on in vitro storage of platelet concentrates

Platelet concentrates were prepared for in vitro storage in either Fenwal PL-732 or Cutter CLX platelet packs. The units were stored at 22 degrees C for seven days with either horizontal or tumbler agitation. Measurement of pH, hypotonic shock response and serotonin uptake indicated in vitro viability was well maintained during 5-7 days storage using either type of pack with either mode of agitation. The longer storage interval did not effect either plasma fibrinogen concentrations or binding of monoclonal antibody, AN51. However, gross contamination of the units with leucocytes caused increased glucose consumption, substantial fall in pH and loss of in vitro viability after five days storage. The work suggests the shelf-life of platelet concentrates can be extended to five days and that they are clinically effective providing the leucocyte contamination is minimised.

Rapid preparation of fresh platelet concentrates from CPD-blood by (mild) acidification

Two methods of preparation of platelet concentrates (PC) derived from citrate-phosphate-dextrose (CPD) whole blood have been compared: (1) resuspension after having left the PC undisturbed at room temperature for 1 h (according to Mourad), and (2) immediate resuspension of the PC after the centrifugation of a platelet-rich plasma which has been acidified beforehand by the addition of ACD. In vitro platelet yield in acidified (CPD/ACD-)PC was at least equal to and, in cases with a particularly strong postcentrifugal tendency for clumping of platelets, clearly better (p less than 0.05) than in the 'Mourad platelets'. The results show that it is possible to produce PC from fresh CPD whole blood without delay. This may be helpful in clinical situations where freshly prepared PC should be available immediately. A special double bag (Fenwal DFX 733) containing CPD-A in the primary bag and 10 ml of ACD in the satellite bag, allows preparation of PC under these conditions in a closed system.

Release of beta-thromboglobulin during the preparation, in vitro storage and cryopreservation of platelet concentrates

Beta-thromboglobulin is a platelet specific protein which is released from platelets during the platelet release reaction. The amount of beta-thromboglobulin released during various conditions of in vitro storage, including cryopreservation, was compared. The results suggest the measurement of beta-thromboglobulin is unlikely to be of use as a quality control assay for monitoring the in vitro viability of stored platelets.

Technical considerations for platelet aggregation and related problems

Platelet aggregation generally is ordered by the physician to evaluate platelet function in hemorrhagic or thrombotic disorders. Malfunction of the platelet may be the result of an intrinsic congenital defect or an acquired problem induced by drugs or certain circulating plasma factors. It is necessary to obtain information from the patient with respect to family history, drug ingestion, physical or mental stress. In addition, other laboratory studies should be obtained to rule out general coagulation disorders affecting the plasma factors. A bleeding time will be helpful in establishing the severity of any platelet dysfunction. Technical considerations with regard to the preparation of the samples are of primary importance in determining platelet aggregation. Aggregating studies require the use of a variety of binding agents. (Studies on shape change, adhesion of platelets, release of platelet granule substance, and or lysis with extrusion of cytoplasmic constituents may be helpful in certain cases.) Instrumentation for platelet aggregation presently is available in many hospitals. The technical factors to be considered for routine aggregation studies include the type and strength of anticoagulant, centrifugation technique used in preparing the platelet-rich and platelet-poor plasma, platelet concentration, time of storage of the sample after venipuncture and after centrifugation, temperature, and the mixing of the sample. In general, critical concentrations of each reagent should be employed to improve the discrimination capability of the assay. Small differences in response may be obliterated by using excessive concentrations of a given reagent. Comparison in response to the test platelets with control platelets is best done at the same time by performing the aggregation in a dual instrument so that handling procedures will be identical and artifactual differences eliminated.

Separation of platelet-rich plasma by modified centrifugal elutriation

The Beckman centrifugal elutriation (CE) system is modified for the separation of platelet-rich plasma (PRP) from human and rabbit blood. The Beckman separation chamber is found inadequate for this purpose, and a new chamber of conical shape has been developed. Optimal flow rate for separating PRP from whole blood with the new chamber of 11.3 ml capacity is 3.5 ml/min while centrifuging at 2500 rpm or 700 g. Collection process takes about 4 minutes. This new process is based on the principle of centrifugal counterflow displacement and filtration, and is different from the CE process which is based on counterflow centrifugation and differential elution. About 90% of total platelets are recovered with this new process. The collected samples are free of leucocytes and contained only a few erythrocytes. Platelets collected by either differential centrifugation (DC) or new procedures are found to be similar in morphological characteristics, both being discoidal. Other characteristics such as aggregation response induced by ADP or epinephrine, serotonin-14C secretion, and survival of autologous platelets in rabbits are also found to be similar. However, ATP release induced by ADP is consistently higher from platelets prepared by our procedure than from those prepared by the DC procedure.

Occurrence of the release reaction during preparation and storage of platelet concentrates

To determine the degree of damage occurring during preparation and storage of platelet concentrates, the percent release of B-thromboglobulin (BTG) and percent leakage of the cytosolic protein lactic dehydrogenase was determined sequentially from phlebotomy to the end of storage for 72 h at 20-24 degrees C. The effect of storage temperature, pH, and radiation was also evaluated. The results showed that during preparation of platelet concentrate a large degree of release was found after resuspension of the platelet button formed after the high-speed centrifugation. During storage the percent BTG release increased from 18.1 to 40.2% (p less than 0.05). The percent release seen during storage at 4 degrees C (72 h) was 19.2%, while that seen for platelets subjected to temperature cycling at 4-37 degrees C was 24.9%. Both of these values were significantly less (p less than 0.05) than that seen for concentrates stored at room temperature. A negative correlation between pH and BTG release was found (r = -0.64). Irradiation to 10,000 rad did not induce the release reaction or lactic dehydrogenase leakage. We conclude that the degree of in vitro platelet release is dependent on the preparative manipulations, and gentler protocols for preparation and storage of platelets should be investigated.

Lack of conformity in the behaviour of platelets during normal storage conditions at 22 degrees C

Platelets prepared from citrate-phosphate-dextrose blood under normal routine conditions and concentrated to 1,000-1,600 x 10(9) x 1(-1) varied considerably in their capacity to acidify the medium. Serotonin uptake was well maintained for 5 days provided that adenosine 5'-triphosphate was within 50% of normal and pH was above 6.0. A strong release of platelet factor 4 was occasionally seen in relation to preparation. In some preparations the platelet factor 4 was well maintained for 5 days, in others a sudden or gradual release was seen during storage. The investigation indicates that differences in the quality of routinely prepared platelets occur during preparation and storage which are insufficiently well explained and controlled.

Preparation and storage of platelet concentrates. I. Factors influencing the harvest of viable platelets from whole blood

Factors affecting the yield and viability of concentrated platelets have been investigated in a blood component programme. It was found that 86+/-1% of the platelets from a unit of whole blood can be concentrated without loss of viability by processing ACD or CPD anticoagulated blood at room temperature. The steps are initial centrifugation at 1000 g for 9 min to harvest platelet-rich plasma; centrifugation of the platelet-rich plasma at 3000 g for 20 min to pack the platelets; and resuspension of the platelet pellet in residual plasma after 1 1/2 h.

Preparation and storage of platelet concentrates

A technique of platelet concentrate preparation and storage is presented which permits the maximum number of viable and functional platelets to be preserved for periods of 72 hours. Although the storage conditions must be followed precisely, the method is nevertheless simple to perform and does not require specialized expensive equipment. Critical factors include: 1) preparation of the platelet concentrates with an initial centrifugation of 1000 X g for 9 minutes and a second centrifugation of 3000 X g for 20 minutes (86% +/- 1 platelet yield), 2) a storage bag composed of either Fenwal's PL-146 or McGaw plastic, 3) constant gentle mixing, 4) a 70 ml residual plasma volume, and 5) room temperature storage (22 C +/- 2). In Vivo platelet recovery after 72 hours of storage at room temperature averaged 46 per cent +/- 3 and survival was 7.9 days +/- 0.3 (81% of fresh platelet viability). The function of these platelets as measured by the correlation between bleeding time and platelet count after transfusion of pooled platelets into unimmunized, aplastic thrombocytopenic recipients was as good as that of fresh platelets. Both viability and function of concentrated platelets stored at 4 C are severely compromised.

Clinical and experimental studies on adenine, various nucleosides and their analogs in hematology

In red blood cells as well as in platelets there appears to be a decrease in adenine nucleotides during storage under blood bank conditions. This can be decreased by use of anticoagulant preservatives with higher phosphate content than the standard ACD solution, through the addition of adenine and inosine. Maintenance of higher ATP levels appears to be related to longer circulating life span after transfusion into patients in the case of red blood cells but not platelets. Inosine and more alkaline preservative medium also contribute to the maintenance of 2,3-DPG levels in red blood cells, and with it to the maintenance of normal hemoglobin dissociation curves and thus oxygen-carrying capacity. Certain nucleoside analogs may contribute to the preservation of platelets and of whole blood by their platelet-aggregation inhibitory activity. Platelet-aggregation inhibitors may also be useful in preventing thromboembolic episodes with potentially greater safety than anticoagulants.

Platelet preservation by freezing. Use of dimethylsulfoxide as cryoprotective agent

Variables important in the preservation of platelets by freezing with dimethylsulfoxide (DMSO) as cryoprotective agent were studied in normal volunteers and thrombocytopenic patients. Use of 5 per cent DMSO and a freezing rate of 1-3 degrees C/minute yielded optimal preservation of platelet viability. The addition of 5 per cent Dextrose did not improve results. In vivo yield using 5 per cent DMSO was superior to previous results in which glycerol was used as the cryoprotective agent. Viability after freezing was equivalent when platelets were frozen in small (10 ml) and large (60 ml) volumes of plasma. The larger volume had the advantage that a smaller percentage of the platelets was lost during transfer from one plastic container to another.