In vitro characteristics of white cell-reduced single-unit platelet concentrates stored in syringes

BACKGROUND: Platelet concentrates (PCs) for premature infants may be subjected to filtration, centrifugation, and various storage conditions before transfusion. STUDY DESIGN AND METHODS: As there are few data on the cumulative effect of these procedures on PCs, platelet properties (including biochemical and functional in vitro assays) were evaluated after the processing of single units of PCs through a 1-unit-capacity high-efficiency white cell (WBC)-reduction filter followed by syringe storage at either 22 or 37 degrees C for 6 hours. Two- and 5-day-old PCs, volume-reduced PCs, and prestorage WBC-reduced PCs were evaluated. RESULTS: WBC filtration consistently resulted in a 3 to 4 log10 reduction in WBCs, with less than 15-percent platelet loss. No adverse effects of platelet function or evidence of increased platelet activation as determined by the percentage of P-selectin positivity were noted. A decrease in pH associated with increased lactate production and consumption of glucose was observed following syringe storage under all conditions tested. Such changes were most pronounced, however, with volume-reduced PCs stored at 37 degrees C (pH 6.31 +/− 0.15, lactate 23.0 +/− 3.06 mmol/L). All pH levels at the end of storage were above the minimum Food and Drug Administration requirement (pH 6.0). CONCLUSION: The in vitro data suggest that single units of PCs can undergo WBC filtration followed by syringe storage for up to 6 hours and still maintain acceptable storage characteristics. The practice of maintaining volume-reduced PCs in syringes for 6 hours at 37 degrees C in isolettes during transfusion should, however, be avoided.     

Logistics of platelet production: platelet concentrate from one-day-old blood stored at 10 degrees C

Platelet concentrates were prepared from blood stored at 18 to 20 hours at either 10 ± 2 degrees C or 16 ± 2 degrees C. Platelets prepared from blood stored at 10 degrees C had good in vitro properties. The results were not distinguishable from those obtained with freshly- isolated platelets. The in vivo effectiveness of platelets prepared in this manner must be established.     

In vitro characteristics and in vivo viability of platelets contained in granulocyte-platelet apheresis concentrate

A paired prospective study was performed to compare the in vitro storage characteristics and in vivo kinetics of platelets stored in granulocyte-platelet concentrates prepared by apheresis with platelets prepared from whole blood. Platelet and granulocyte-platelet concentrates were collected from five healthy volunteer autologous donors and stored for 16 to 18 hours at 20 to 24 degrees C with and without agitation, respectively. After storage, pH, platelet count, percent release of beta-thromboglobulin, morphologic score, and percent osmotic recovery were measured. In addition, the granulocyte-platelet concentrates were assayed for total leukocyte count, release of lysozyme, and by several in vitro tests of granulocyte function. The platelets in both products were labeled with 111In oxine and infused into the donors. The pH of both products was above 6.0 at the end of storage. The units stored as platelet concentrates compared with those stored as granulocyte-platelet concentrates showed a higher percent release of beta-thromboglobulin, 18.4 +/- 4.0 percent versus 5.9 +/- 3.2 percent (mean +/- SD), but significantly better morphologic scores, 676 +/- 21 versus 525 +/- 56, and better osmotic recovery scores, 72 +/- 10 percent versus 40 +/- 7 percent, respectively (all p less than 0.05). The platelet concentrates (compared with the granulocyte-platelet product) had significantly better in vivo recovery, 49.5 +/- 15.8 percent versus 38.9 +/- 11.5 percent, and survival, 6.1 +/- 1.3 days versus 2.4 +/- 0.4 days, respectively (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

In vitro and in vivo quality of leukoreduced apheresis platelets stored in a new platelet additive solution

BACKGROUND: Platelets (PLTs) stored in additive solutions (PASs) may reduce the risk of several plasma‐associated adverse transfusion reactions such as allergic reactions and potentially transfusion‐associated lung injury. The objective of this study was to determine the in vitro characteristics and the in vivo radiolabeled recovery and survival of apheresis PLTs (APs) stored in a new PAS and compare the latter to Food and Drug Administration (FDA) criteria. STUDY DESIGN AND METHODS: Hyperconcentrated APs were collected from healthy subjects in a paired crossover study comparing PAS (35% plasma) and 100% plasma‐stored APs (Part 1) up to 7 days and, in Part 2, to determine the in vivo recovery and survival of PAS stored AP at 5 days compared to fresh PLT controls. In vitro and in vivo assays were performed following standard methods. RESULTS: Sixty‐six and 25 evaluable subjects successfully completed Parts 1 and 2, respectively. pH for PAS AP was maintained above 6.6 for 5 days of storage. P‐selectin values were consistent with published values for commonly transfused PLT products. The PAS in vivo PLT recovery (54.3 ± 8.1%) was 86.7% of the fresh control, and survival (6.4 ± 1.3 days) was 78.0% of the fresh control, both meeting the FDA performance criteria. CONCLUSION: APs stored in PAS with 35% plasma carryover maintained pH over 5 days of storage and met current FDA criteria for radiolabeled recovery and survival. The use of PAS for storage of single‐donor PLTs in clinical practice represents an acceptable transfusion product that reduces the volume of plasma associated with PLT transfusion.     

Ultraviolet irradiation of platelet concentrate abrogates lymphocyte activation without affecting platelet function in vitro

We studied the effect of ultraviolet (UV) radiation on platelet concentrates. Samples irradiated at 310 mm for 30 minutes at a dose of 1782 J per m2 showed no loss of platelet function in vitro as determined by adenosine diphosphate, collagen, or ristocetin-induced aggregation. Lymphocytes isolated from irradiated units were unable to act as responders or stimulators in a mixed-lymphocyte reaction. These data suggest that UV radiation of platelet concentrates may result in a cell suspension that is unable to evoke an immunological response.     

In vitro metabolism of packed erythrocytes stored in CPD-adenine

In vitro metabolism of erythrocytes packed at 70 and 90 per cent hematocrits and stored in various CPD-adenine preservatives was studied. It was found that maintenance of acceptable levels of adenosine triphosphate (ATP) for the full 42 days of storage could be accomplished only if glucose levels were doubled from the standard 138.7 mM concentration to 277.5 mM level. If glucose levels were doubled, the amount of adenine could be decreased from 4.07 mM (0.50 mM final concentration) to 2.04 mM (0.25 mM final concentration) with maintenance of ATP at greater than 2.0 mumoles/g Hb. 2,3- diphosphoglycerate concentrations were essentially absent by 21 days in the various media studies. Thus, in vitro levels of ATP appear to be maintained at acceptable levels in a CPD media modified to contain 2 times glucose and 2.04 mM adenine.     

In vitro evaluation of platelets stored in CDP-adenine formulations

Little information is available about the effect of adenine and added glucose on stored platelets. Two new formulations, CPDA-2 and CPDA-3, contain 34 mg adenine per 63 ml preservative and extra glucose (1.75 and 2.0 times the glucose in standard CPD). We have studied the in vitro integrity of platelet concentrates stored in CPD, CPDA-1, CPDA-2, and CPDA-3 at 22 C for 72 hours. Morphology score, pH, platelet size, population distribution parameters, and electron microscopic ultrastructure did not show any adverse effects which could be ascribed to the presence of adenine or extra glucose or both. No differences in platelet adenosine triphosphate (ATP) concentration or plasma glucose utilization during storage were found between CPD and CPDA-1 platelets. The results suggest that adenine and added glucose in these preservatives are not detrimental to platelets in vitro by the measures employed.     

Growth of bacteria in prefilled syringes stored in home refrigerators

Insulin was examined for the rate of bacterial growth after being stored in prefilled syringes in home refrigerators and in a controlled laboratory refrigerator. Home refrigerators were used to simulate conditions that exist in client homes to establish the safety of storing insulin in prefilled syringes in uncontrolled environments. Insulin from each source was inoculated on three different media and incubated at three temperatures in three oxygen environments. A total of 768 cultures were examined. It was found that temperature had a significant effect on the incidence of bacteria. The difference in incident of bacteria between syringes stored in the controlled versus uncontrolled environments was not statistically significant.     

In vitro assessment of platelet function

With the realization that the skin bleeding time is often an unreliable measure of platelet function, efforts have been made to identify ways to assess qualitative platelet dysfunction. Currently available techniques measure platelet adhesion, platelet aggregation, the ability of platelets to retard or stop flow through filters, and the contribution of platelets to in vitro clot formation. Glass bead adhesion, which continues to be performed in some laboratories, is gradually being replaced by measures of platelet adhesion to filters composed of glass fibers, Dacron fibers, or collagen. In each instance, anticoagulated platelet-rich plasma or whole blood flows through the filter under a regulated pressure gradient. The amount of blood flowing through the filter versus time and/or the time to filter occlusion are measured. Recent developments in platelet aggregation have focused on whole blood and stagnation point flow aggregation techniques. Whole blood aggregation does not require blood sample processing and accommodates blood obtained from citrated vacutainer tubes. Stagnation point flow measures both platelet adhesion and aggregation and may be able to detect pathologically-enhanced platelet function. Global measures of hemostasis attempt to simultaneously evaluate the adequacy of fluid phase coagulation and platelet function. Currently available techniques include Thromboelastography, SonoClot Analyzer, Hemodyne Hemostasis Analyzer, PITT, and Hemostatometry. Although each of these technologies have been shown to provide interesting data in the research setting, the ability of any of these techniques to detect abnormal or clinical inadequate platelet function remains to be established.     

Chemokines in stored platelet concentrates

BACKGROUND: Platelets contain several mediators, belonging to a family of proinflammatory cytokines named chemokines, that are stored in the organelles. Release and accumulation of these chemokines during storage of platelet concentrates (PCs) might be responsible for nonhemolytic transfusion reactions. STUDY DESIGN AND METHODS: Analysis was done of pH and the levels of platelet factor 4, beta-thromboglobulin, interleukin 8, RANTES, macrophage-inflammatory protein-1 alpha, lactate dehydrogenase, and serotonin in the supernatant of stored PCs on Days 1, 3, 5, and 8. PCs were prepared by apheresis or from pools of four buffy coats. Buffy coat PCs were filtered before storage. RESULTS: Nonfiltered apheresis PCs, which had a higher white cell contamination (p < 0.01), contained significantly more platelets than did buffy coat PCs (p = 0.02). The pH decreased significantly in apheresis PCs (p = 0.01), whereas there was a significant increase in lactate dehydrogenase (p < 0.001). In buffy coat PCs, pH remained stable and lactate dehydrogenase increased moderately. Concentrations of platelet factor 4 and beta-thromboglobulin increased steadily in both preparations over the storage period (p < 0.001). Macrophage- inflammatory protein-1 alpha was hardly detectable in the supernatant of both PCs, while RANTES levels increased significantly with storage time (p < 0.001). Interleukin 8 was not found in the supernatant of any PCs, with the exception of one apheresis PC with high white cell contamination (> 10(9)/ L). Serotonin levels were higher in apheresis PCs (p = 0.01), but the levels did not correlate with storage time. CONCLUSION: Platelet factor 4, beta-thromboglobulin, and RANTES were released from platelets during storage and accumulated over time in the PCs. These chemokines might play a causative role in nonhemolytic transfusion reactions because of their inflammatory potential, but the clinical effects of the transfusion of PCs with high chemokine contents remain to be investigated.     

Elimination of cytokine production in stored platelet concentrate aliquots by photochemical treatment with psoralen plus ultraviolet A light

BACKGROUND: Cytokines generated in platelet concentrates (PCs) during storage have been implicated as possible mediators of febrile nonhemolytic transfusion reactions. Two potential methods of white cell inactivation were compared for their ability to reduce cytokine synthesis in pooled random-donor PC aliquots: treatment with gamma-radiation and photochemical treatment (PCT) using psoralens and ultraviolet A light. STUDY DESIGN AND METHODS: ABO-matched PC aliquots were pooled and divided into separate aliquots. Aliquots (20 mL) were taken from each pool to serve as an untreated control and to undergo gamma-radiation. Aliquots were treated by using either gamma-radiation (2500 or 5000 cGy) or virucidal PCT. PCT with the psoralens 8-methoxypsoralen (8-MOP), aminomethyltrimethyl psoralen (AMT), and S-59 was investigated. PC aliquots were stored for 7 days and analyzed for levels of interleukin 8 by use of an enzyme-linked immunosorbent assay. Levels of DNA adduct formation were determined by using 3H-labeled psoralens. RESULTS: Levels of interleukin 8 in the untreated random-donor PC aliquots increased with increasing white cell counts, but they were not affected by pooling. The untreated control aliquots and the aliquots treated with gamma-radiation had significant increases in levels of interleukin 8 after 5 to 7 days of storage (p<0.05). PCT with S-59 resulted in a significant reduction in cytokine synthesis (p<0.05). Day 5 to 7 levels of interleukin 8 did not differ significantly from Day 0 levels. Inhibition of interleukin 8 production by PCT increased with increasing levels of DNA modification (S-59 > AMT > 8-MOP). CONCLUSION: PCT that utilizes S-59 has been developed to inactivate potential viral and bacterial pathogens in PC aliquots while maintaining in vitro platelet function. These data demonstrate that PCT of aliquots of pooled PC aliquots before storage also prevents white cell cytokine synthesis during storage. PCT may therefore offer the potential for reducing cytokine-associated febrile nonhemolytic transfusion reactions.     

In vitro evaluation of platelet concentrates, prepared from pooled buffy coats, stored for 8 days after filtration

BACKGROUND: Posttransfusion complications can be prevented by pretransfusion removal of donor white cells from platelet concentrate. The filtration used for this removal seems to have little effect on platelet function and activation, but more information is needed on its effect on function during subsequent long-term storage of concentrate. STUDY DESIGN AND METHODS: The effect of prestorage filtration of buffy coat-prepared platelet concentrates (PCs) on platelet function, metabolism, and activation was investigated. A pool of three PCs, each made of four buffy coats, was split into three equal volumes; two were filtered over two different filters and the third served as a control. Variables monitored immediately after filtration and during the subsequent 8-day storage period at 22 degrees C included aggregation upon stimulation with collagen and/or ADP, platelet adhesion capacity to collagen and fibrinogen in flowing blood, nucleotide content of and nucleobase release by the platelets, expression of activation-dependent antigens, and beta-thromboglobulin release by the platelets. RESULTS: No differences were observed between the PCs filtered over two different filters and the nonfiltered control PCs immediately after filtration and during storage, except for a selective removal (20%) of beta-thromboglobulin by one filter. CONCLUSION: PCs prepared from a pool of four buffy coats can be filtered and subsequently stored for 8 days (starting +/− 24 hours after whole blood collection) without detriment to platelet function, metabolism, or activation.     

In vitro properties of platelets stored in three different additive solutions

BACKGROUND: New platelet (PLT) additive solutions (PASs) contain compounds that might improve the storage conditions for PLTs. This study compares the in vitro function, including hemostatic properties (clot formation and elasticity), of PLTs in T‐Sol, Composol, or SSP+ during storage for 5 days. STUDY DESIGN AND METHODS: Fifteen buffy coats were pooled and divided into three parts. PLT concentrates (PCs) with 30% plasma and 70% PAS (T‐Sol, Composol, or SSP+) were prepared (n = 10). Swirling, PLT count, blood gases, metabolic variables, PLT activation markers, and coagulation by free oscillation rheometry (FOR) were analyzed on Days 1 and 5. RESULTS: Swirling was well preserved and pH acceptable (6.4‐7.4) during storage for all PASs. Storage of PLTs in T‐Sol led to a decrease in PLT count whereas the number of PLTs was unchanged in Composol or SSP+ PCs. PLTs in T‐Sol showed higher glucose metabolism than PLTs in Composol or in SSP+. At the end of storage PLTs in T‐Sol had higher spontaneous activation and lower ability to respond to an agonist than PLTs in Composol or SSP+. PLTs in all the PASs had a similar ability to promote clot formation and clot elasticity. CONCLUSION: Storage of PLTs in Composol or in SSP+ improved the quality of PCs in terms of better maintained PLT count, lower glucose metabolism, lower spontaneous activation, and improved response to a PLT agonist compared to PLTs in T‐Sol. PLTs stored in the various PASs had similar hemostatic properties. These findings make Composol and SSP+ interesting alternatives as PASs.     

Extension of platelet concentrate storage

Extension of the storage time of platelet concentrates in a satellite bag which is part of a new blood bag system was studied by reinfusing autologous 51Cr-labeled platelets into normal volunteers, and measuring postinfusion platelet counts and bleeding times in patients requiring platelet transfusions. This satellite bag, made of polyvinylchloride plasticized with a new agent, was found to protect platelet concentrates against fall of pH better than other containers studied. This protection was felt to be due to the greater gas permeability of the new plastic. Mean in vivo recovery and half-life (greater than 31% and 3.3 days, respectively) of autologous reinfused platelets were satisfactory following 5 days of storage. Following 7 days of storage, mean recovery was 41 percent and half-life was 2.8 days. Peripheral platelet count increments in patients following platelet transfusions with concentrates stored 4 to 7 days in the new plastic were comparable to increments following transfusion of platelets stored 2 to 3 days in the other plastics studied. Bleeding times shortened in three of four patients receiving platelet concentrates stored from 4 to 6 days in the new plastic. Platelet concentrates stored in the new bag at 20 to 24 degrees C with flat-bed or elliptical agitation could be transfused for up to 5 days following phlebotomy with acceptable clinical results. The new plastic container is promising for storage of platelet concentrates for up to 7 days. Due to the higher pH of 50-ml platelet concentrates stored in bags made with the new plastic, the concentrates were superior at any storage interval to those stored in bags made of the other plastics studied.     

In vitro function and in vivo viability of stored platelet concentrates. Effect of a secondary plasticizer component of PVC storage bags

Previous studies have shown that CL-2399 (Cutter) and PL-130 (Fenwal) polyvinyl chloride (PVC) plastic bags are unsatisfactory for storage of platelet concentrates (PC) at 22 degrees C. In an effort to explain the effects of plastic bags, the chemical make-up of CL-2399 and PL-130 PVC films was determined and compared with that of P1-146 (Fenwal) PVC, which is satisfactory for PC storage at 22 degrees C. The only significant difference between the three materials was the incorporation of tetrahydrofurfuryl oleate (THFO) as a secondary plasticizer in CL-2399 and PL-130. The response of platelets to aggregating agents, uptake of serotonin, recovery from hyptonic stress, and serotonin release during storage following storage in a modified CL- 2399 plastic prepared without THFO and designated CL-3000 (Cutter) was equivalent to PL-146 and far superior to CL-2399. In vivo studies in two laboratories of platelets stored in CL-3000 bags showed satisfactory recovery (56 +/− 4.2% and 46.7 +/− 2.7%) and survival (6.4 +/− 0.4 days and 7.4 +/− 0.6 days). From these studies we conclude that the THFO secondary plasticizer component of PL-130 and CL-2399 is the cause of the poor platelet viability of platelets stored in these plastic bags. The mechanism of impairment is not known. The causative agent(s) may be degradation products of THFO (formed during manufacture of the PVC film) that are leached from the plastic into PC during storage.     

Complement activation in stored platelet concentrates

Activation of platelets during preparation and/or storage of platelet concentrates in plastic containers at room temperature has recently been recognized. Many different biologic causes of this activation have been postulated. Activated complement, as a multi-enzyme system, is one of the possible sources of molecules leading to platelet activation. To detect complement activation, functional complement activity and the generation of complement-derived ligands were investigated in platelet concentrate supernatant plasma during 5 days of storage at room temperature. Hemolytic tests for functional classical and alternative pathway activity were used, as was the kinetic test for complement- mediated inhibition of immune complex precipitation. The presence of C3 activation products (C3, C3c, C3dg) was investigated in plasma by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting procedures and on platelets by immunofluorescence. Activation of complement was evident during storage, and C3c and C3d fragments were clearly demonstrated in plasma. The amount of C3d fragments on platelets gradually rose during the first 3 days of storage. At the end of 5 days of storage, the platelets became C3d negative. There are two possible mechanisms of C3d disappearance–shedding and/or further degradation of C3d fragments. Those results indicated that complement activation and the generation of complement-dependent ligand-receptor interaction may be mechanisms for platelet activation in concentrates stored at room temperature.     

Cytokine generation in stored platelet concentrates

BACKGROUND: Cytokines, because of the nature of their immunoinflammatory actions, are potential mediators of the symptom complex of nonhemolytic transfusion reactions. One possible source of cytokines in the transfusion setting is the stored blood component itself. STUDY DESIGN AND METHODS: To test this possibility, the plasma portion of stored platelet concentrates (PCs) was assayed for the presence of interleukins 1 beta (IL-1 beta), 6 (IL-6), and 8 (IL-8) and tumor necrosis factor alpha (TNF-alpha). Samples were taken from PCs obtained from the inventory of a regional blood center (n = 120; 30 each of 2-, 3-, 4-, and 5-day-old units). RESULTS: Detectable levels of IL-8 were measured in 59 percent of the PCs sampled, ranging from 30 percent of the 2-day-old units to 83 percent of the 5-day-old units. The median IL-8 concentration ranged from undetectable levels in 2-day- old units up to 1100 pg per mL in 5-day-old units. The mean IL-8 concentration in 5-day-old units, 11,600 pg per mL, was 100 times the mean for 2-day-old units, which was 116 pg per mL (p < 0.0001). The highest levels of IL-8, 50,000 to 200,000 pg per mL, in general were found in units with the longest storage times and highest white cell counts. Sequential sampling of 17 individual PCs over 7 days of storage confirmed that IL-8 increases progressively with increasing storage time. Parallel, but smaller, increases in IL-1 beta were observed in those units with high IL-8 concentrations. TNF-alpha was detected in 3 (10%) of 30 five-day-old PCs, but never exceeded 55 pg per mL in any unit tested. IL-6 at levels of 740 and 508 pg per mL was detected in two 5-day-old units with high white cell counts of 9500 and 14,800 per microL, respectively, but not in 21 additional units tested with white cells < or = 9200 per microL or storage time of < or = 2 days. White cell reduction by third-generation filters on Day 1 of platelet storage prevented the generation of IL-8 and IL-1 beta to Day 5 of storage. CONCLUSION: Although IL-8 achieved levels in some units of PCs that appear capable of causing physiologic changes, the potential adverse effect on transfusion recipients of the infusion of cytokines in PCs remains to be investigated.     

The in vitro effect of recombinant factor VIIa on coated platelet formation and clot dynamics of stored platelet concentrates

BACKGROUND: Storage can negatively impact the hemostatic potential of platelet concentrates (PCs) used for transfusion. At the site of vascular injury, normal platelets (PLTs) are hypothesized to change into highly procoagulant-coated PLTs upon costimulation with collagen and thrombin. We investigated whether activated recombinant factor VII (rFVIIa, NovoSeven, Novo Nordisk A/S) could improve the ability of stored PLTs to support coagulation under conditions that promote the formation of coated PLTs.
STUDY DESIGN AND METHODS: PCs stored for 1, 4, 6, and 8 days were costimulated with thrombin and with convulxin, a collagen glycoprotein VI receptor agonist, to create coated PLTs. The effect of rFVIIa on the ability of stored PCs to form coated PLTs, generate thrombin, and impact clot dynamics was evaluated by flow cytometry, a plasma-based assay, and thrombelastography, respectively.
RESULTS: Coated PLT formation decreased significantly with increasing storage time (80% vs. 50%-55%, p < 0.05), and this was not affected by the addition of rFVIIa. rFVIIa accelerated thrombin generation (p < 0.001) and clot formation (p < 0.001) and significantly increased thrombin generation throughout the storage period (p < 0.001). Resistance to fibrinolysis was impaired at the end of storage, and this was not affected by the addition of rFVIIa.
CONCLUSION: rFVIIa accelerated thrombin and clot formation throughout storage, with the most pronounced effect observed in the PCs that had been stored for the shortest length of time (Day 1). Resistance to fibrinolysis was gradually impaired throughout the storage period and was not affected by the addition of rFVIIa.     

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

BACKGROUND: In the United States, apheresis platelets (PLTs) are suspended in autologous plasma. PLT additive solutions, long used in Europe, decrease recipient allergic reactions and may reduce the risk of transfusion‐related acute lung injury. We evaluated Amicus‐collected PLTs stored in platelet additive solution (PAS) III (InterSol) for 5 days. STUDY DESIGN AND METHODS: In Study 1, 71 subjects donated two products on a single day—one each stored in 100% plasma or 65% PAS III/35% plasma. Products underwent standard in vitro testing on Days 1 and 5. In Study 2, 43 additional subjects provided Amicus products stored for 5 days in 65% PAS III/35% plasma for in vivo radiolabeled recovery and survival determinations. The effect of approximately 2500 cGy Day 1 gamma irradiation was evaluated in a subset of products. RESULTS: PAS III PLTs (n = 70) had a median Day 5 pH_22°C of 7.2 (lower 95%, 95% tolerance limit, 6.9). Mean Day 5 recovery and survival of radiolabeled PAS III PLTs (n = 33) were, respectively, 80.5 and 72.1%, of fresh autologous PLTs. With 95% confidence, these values were at least 66% of fresh PLT recovery and 58% of survival. All in vitro variables remained within ranges seen in licensed products for irradiated and nonirradiated PAS III PLTs. CONCLUSION: Leukoreduced Amicus PLTs stored in 65% PAS III/35% plasma in PL‐2410 containers maintained pH ≥ 6.9 throughout 5 days' storage. Radiolabeled PLT recovery and survival values met US Food and Drug Administration statistical criteria. Gamma‐irradiated PAS III PLTs demonstrated no significant adverse effects due to irradiation in in vitro testing.