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 × g for 9 minutes and a second centrifugation of 3000 × 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.     

Comparative Studies of the Viability of Human Platelets Stored at 4 C in Plastic and Glass Containers

Studies were done to investigate whether the surface of the container (plastic or glass) would influence the viability of human platelets stored at 4C for short intervals.
Cr⁵¹-labeled platelets prepared as concentrates suspended in plasma were preserved at 4 C for 24, 48 or 72 hours and their capacity to recirculate and survive after infusion into the respective donors ("viability") was determined. In addition, the clot retraction property of the stored platelets was measured.
Platelet viability was sharply reduced after storage at 4 C in all experiments. When the storage period was limited to 24 hours, survival curves of platelets preserved in plastic bags were similar to those of platelets preserved in glass bottles. However, after 48 hours of storage, viability of platelets preserved in plastic containers had values significantly higher than those of platelets preserved in glass containers. After 72 hours of storage, platelet viability was reduced to minimal values but was still greater for platelets stored in plastic bags.
The study of clot retraction confirmed data previously obtained and showed that this platelet property was preserved better by storage in glass bottles rather than in plastic bags. Platelet viability was, however, lost very rapidly during storage at 4 C in either type of container so that the unfavorable effect of plastic on the preservation of clot retraction was thought not to be of practical importance in platelet transfusion therapy.     

Circulation of Concentrated One‐day‐old Platelets in Vivo

Platelet concentrates of rat and human origin were stored at 22 C or at 4 C for up to 24 hours without additives. Transfusion of these concentrates into thrombocytopenic recipients demonstrated that: (1) storage of rat or human platelets at 4 C for up to 24 hours did not affect their recovery in vivo ; (2) storage at 22 C resulted in a marked reduction in the viability of rat platelets but only a slight reduction in the viability of human platelets as adjudged by these criteria; (3) at 24 hours posttransfusion, the residual increment of platelets stored at 22 C was significantly higher than that of platelets stored at 4 C. The pH of the concentrates (rat and human) stored at 4 C remained slightly alkaline while the pH of those stored at 22 C., especially rat platelets, was significantly reduced. The deleterious effects of storage of platelets at 4 C are well known. These effects, however, do not preclude their usefulness when a limited objective of arresting or preventing hemorrhage for short periods is pursued. When daily platelet transfusions are feasible, platelets stored for 24 hours at 4 C in the absence of fresh material are adequate for clinical use.     

Platelet Response to Hypotonic Stress after Storage at 4 C or 22 C

We have studied the response of platelets to a standardized osmotic stress following storage at either 4 C or 22 C. Platelets that had been stored at 22 C for up to 72 hours retained their ability to recover from hypotonic swelling, while those that had been stored at 4 C showed a rapid decline in their ability to recover from hypotonic stress.     

Studies on platelets exposed to or stored at temperatures below 20 degrees C or above 24 degrees C

BACKGROUND : Platelet concentrates (PCs) may be subjected to temperatures outside 20 to 22 degrees C during shipping or storage, which may have an adverse effect on platelet quality. STUDY DESIGN AND METHODS : These studies systematically evaluated the effect of short- term exposure (≤ 24 hours) of platelets to temperatures above 22° or below 20° C as part of standard 5-day PC storage at 22° C, as well as the effect of long-term storage (5 days) at 24 and 26° C. For the short-term exposure studies, up to 6 units of Day 1 standard PCs were mixed, split, and returned to the containers. Test units were then stored without agitation in an incubator at a specific temperature (4, 12, 16, or 18° C) for various times up to 24 hours, after which they were stored with agitation at 22° C. One unit acted as control and was stored at 20 to 22° C throughout the 5-day storage period. Loss of platelet discoid shape was determined photometrically by the extent of shape change assay, by an increase in apparent platelet size by morphologic evaluation, and by swirling. RESULTS : A gradual loss of platelet discoid shape occurred at temperatures below 20° C. For similar periods, a greater difference between test and control PCs was observed in units held at 4° C than in those held at 16° C. The data were fitted to an equation to relate platelet discoid shape (% of control) to exposure temperature and time. Assuming that a 20-percent decrease or more in the extent of shape change assay represents a significant loss in platelet viability, the equation predicts that such a loss occurs when the platelets are exposed to 16° C for ≥16 hours, to 12° C for ≥10 hours, or to 4°C for ≥6 hours, whereas exposure to 18° C for ≤24 hours has no significant effect. Storage for 5 days at temperatures ≤26° C was not associated with any significant reduction in platelet discoid shape or other measures of platelet quality. CONCLUSION : There was a gradual loss of platelet discoid shape at exposure temperatures < 20°C, which worsened as temperatures decreased and exposure times increased to 24 hours. This relationship can be described in an equation that could be used as a guideline for allowable exposure conditions.     

Recovery, lifespan, and function of CPD-Adenine (CPDA-1) platelet concentrates stored for up to 72 hours at 4 C

We studied the in vivo recovery, lifespan, and hemostatic effectiveness of CPDA-1 platelet concentrates stored for up to 72 hours at 4 C. A total of 120 CPDA-1 concentrates containing an average (+/− 1 S.D.) of 6.6 +/− 2.0 × 10(10) platelets were prepared. The pH of the units following storage at 4 C was 6.8 +/− 0.2; no unit had a pH below 6.3. Autologous transfusion of six normal volunteers showed that platelets stored at 4 C for 72 hours had an in vivo recovery of 40 +/− 18 per cent and a lifespan of 5.1 +/− 1.5 days. The hemostatic effectiveness of CPDA-1 platelets was determined by platelet counts and template bleeding time measurements in 10 thrombocytopenic patients. Patients receiving 48-hour-stored platelets had a four- to six-hour posttranfusion corrected platelet increment averaging 15,300 +/− 3,200/microliter which was 67 +/− 34 per cent of expected recovery. Four of the five patients transfused with this preparation showed an improved bleeding time. In contrast, three patients receiving 72-hour- stored platelets had a four- to six-hour posttransfusion increment of 5,800 +/− 2,400/microliter that was only 26 +/− 13 per cent of the expected recovery; furthermore, only one of these patients showed any correction of the bleeding time. These data indicate that CPDA-1 platelets are hemostatically effective when stored at 4 C for up to 48 hours.     

Effective storage of granulocytes collected by centrifugation leukapheresis from donors stimulated with granulocyte-colony-stimulating factor

BACKGROUND: Donor stimulation with granulocyte-colony-stimulating factor (G-CSF) has increased the number of neutrophils (PMNs) that can be collected for granulocyte transfusion therapy. Clinical utility, however, has been limited by the inability to store functional PMNs ex vivo. This study was conducted to determine whether granulocyte products from G-CSF-stimulated donors could be effectively stored at reduced temperature (22 degrees C vs. 10 degrees C) with maintenance of functional properties in vitro and in vivo. STUDY DESIGN AND METHODS: Nine normal subjects received G-CSF (600 microg subcutaneously) 12 hours before centrifugation leukapheresis. Granulocyte products were divided and stored for 24 and 48 hours under four conditions: 1) 22 degrees C; 2) 22 degrees C, with supplemental G-CSF (100 ng/mL); 3) 10 degrees C; and 4) 10 degrees C, with supplemental G-CSF. Functional PMN activity during ex vivo storage was assessed in vitro and in vivo by the skin-window technique for granulocytes stored at 10 degrees C for 24 hours. RESULTS: Surface expression of CD11b/CD18, CD14, CD16, CD32, and CD64 was maintained during 48-hour storage at reduced temperature. Inducible respiratory burst activity, bactericidal activity, and fungicidal activity were preserved during storage for 48-hour storage at 10 degrees C. Proinflammatory cytokine production was decreased in product stored at 10 degrees C. Supplemental G-CSF ex vivo did not substantially improve functional activity during storage. After storage at 10 degrees C for 24 hours, in vitro chemotactic potential was maintained, and transfused granulocytes retained capacity to circulate and migrate appropriately in vivo. CONCLUSIONS: Granulocyte product collected by centrifugation leukapheresis from G-CSF-stimulated donors can be effectively stored at subphysiologic temperature for 24 hours with preservation of functional activity. Storage at 10 degrees C appears to be slightly superior to storage at 22 degrees C.     

Circulation and hemostatic function of autologous fresh,liquid-preserved,and cryopreserved baboon platelets transfused to correct an aspirin-induced thrombocytopathy

BACKGROUND: The survival of fresh and preserved platelets has been used primarily to determine their therapeutic effectiveness. The function of the fresh and preserved platelets has been difficult to assess. In stable thrombocytopenic patients, platelet function of fresh and preserved allogeneic platelets is evaluated by the reduction in bleeding time. In this study of healthy male baboons, both the survival and function of autologous fresh, liquid-preserved, and cryopreserved platelets in the correction of an aspirin-induced thrombocytopathy was evaluated. STUDY DESIGN AND METHODS: Five healthy male baboons were studied on eight occasions over a 4-year period. To produce a prolonged bleeding time, the baboon was administered 325 mg of aspirin 18 hours before receiving autologous transfusion. The fresh, liquid-preserved, and previously frozen washed platelets were labeled with (111)In-oxine before autologous transfusion. The autologous, nonaspirinated platelets' ability to reduce the aspirin-induced prolonged bleeding time and increase the shed blood thromboxane B2 level at the template bleeding time site was studied. RESULTS: Platelets stored at 22 degrees C for 48 hours had in vivo recovery values similar to those platelets stored for 18 hours, and they significantly reduced the bleeding time and increased the shed blood thromboxane level after transfusion. Platelets stored at 22 degrees C for 72 hours had in vivo recovery values similar to those platelets stored for 18 hours, but the bleeding time was not corrected after transfusion, although there was a significant increase in the shed blood thromboxane B2 level. The cryopreserved platelets significantly reduced the bleeding time and significantly increased the shed blood thromboxane level after transfusion. Cryopreserved platelets had better in vivo survival and function than the 5-day liquid-stored platelets. CONCLUSIONS: The survival of autologous fresh, liquid-preserved, or cryopreserved platelets did not correlate with their function to reduce an increased bleeding time in baboons treated with aspirin.     

The effect of platelets and red cells on granulocytes stored at 22 degrees C

Granulocyte concentrates contain varying numbers of platelets and red cells depending upon the method of collection. Either platelet or red cell concentrations may be as high as 2.0 × 10(12) per I. Studies were done on unwashed and washed granulocyte concentrates and on pure granulocyte suspensions with known numbers of platelets or red cells added. These suspensions or concentrates were stored for 72 hours at 22 degrees C. In both experiments, the following were measured: leukocyte and absolute granulocyte counts, dye exclusion, chemotaxis, plasma glucose, plasma pH, and osmolality. Red cell contamination did not adversely effect granulocyte storage. Platelets, however, did contribute to the functional deterioration of stored granulocytes. In the presence of high concentrations of platelets, both granulocyte dye exclusion and chemotaxis were adversely affected at 48 hours of storage. In another experiment, fresh autologous granulocytes incubated for 18 hours in hydroxyethyl starch-citrated-plasma obtained from stored granulocyte concentrates showed a progressive decrease in chemotaxis related to the age of the stored plasma. Glucose supplementation of the spent plasma maintained chemotactic activity. Contamination of granulocyte concentrates with other cells and the availability of glucose to granulocytes are variables affecting the short-term liquid storage of granulocytes at 22 degrees C.     

Lack of adverse effect of transportation on room temperature stored platelet concentrates

The ability of platelet concentrates stored at room temperature to withstand transportation after removal from the rotator and ideal temperature environment was studied by reinfusing autologous 51Cr- labeled platelets obtained from normal volunteers. Periods of up to 6 hours off the rotator and not under temperature control did not result in a significant change in platelet viability. Platelets transported up to 12 hours after 24 hours of storage and then placed on a rotator for the remainder of the 72-hour storage interval also showed expected recovery and survival. Thus, room temperature stored platelets may be used even when transportation for up to 6 hours is required before the concentrates are transfused.     

Studies on Stored Whole Blood

Blood stored at 10 C displayed no more evidence of cell destruction in vitro than did blood stored at 4 C. Agitation for one hour at weekly intervals of storage was also not obviously damaging, nor was warming blood to 22 C for up to 16 hours. Exposure to 22 C for 24 hours led to erythrocyte deterioration that was most evident when units were more than 21 days old, and agitation plus this warming increased these signs of damage. Units stored as packed cells were moderately affected by exposure to 22 C for 24 hours, and agitation reinforced this effect. Posttransfusion survival of blood warmed to 22 C for 24 hours tended to be lower than nonwarmed controls; the warmed group average was below 70 per cent survival at 28 days of storage.
From these studies, the temperature variation commonly encountered in clinical blood banking (4 C to 10 C and short exposure to 22 C prior to transfusion) would not appear to contribute significantly to erythrocyte damage unless the units were in the oldest stages of storage or had been exposed to warm temperatures for longer than 24 hours. Mechanical stress had minimal adverse effect, but this became more evident when blood was stored as packed cells or when whole blood had been stored for 21 days.     

Aggregation response of human platelets stored at 22 C as platelet-rich plasma

The aggregating response of human platelets stored at 22 C for 72 hours has been studied. Platelets were stored as platelet-rich plasma in order to maintain the plasma pH essentially constant. The response to ADP and collagen decreased with time, but the decrease was less with relatively high concentrations of the aggregating agents. The response to the ionophore A23187 was essentially unaltered during the storage period. Synergistic aggregation with combinations of ADP, collagen and ionophore A23187 was observed with platelets stored for 72 hours under conditions where singly each of the stimuli caused little or no effect. Stored platelets underwent reversible aggregation over a wide range of ADP concentrations but irreversible aggregation was observed in the presence of nonaggregating concentrations of collagen or ionophore A23187. The inhibition of aggregation by PGE1 or cyclic AMP was facilitated as a result of storage. It is suggested that the decreased response toward ADP and collagen reflects a reduced ability on the part of the platelets to mobilize calcium.     

P-selectin mRNA is maintained in platelet concentrates stored at 4°C

BACKGROUND: Platelets (PLTs) contain mRNA and synthesize proteins in response to activation. Most guidelines for PLT concentrates (PCs) recommend ambient temperature for storage but the impact of the storage temperature on PLT mRNA content has not yet been investigated.
STUDY DESIGN AND METHODS: Ten leukoreduced apheresis PCs were split and stored at 22 and 4°C. P-selectin mRNA, its expression on PLTs, and its soluble form were quantified. In parallel, cellular (cell count, mean PLT volume), metabolic (pH, pO₂, pCO₂, HCO₃, glucose), and functional markers (swirling, hypotonic shock response, aggregation to collagen) were analyzed. Rotation thrombelastography was used to monitor the hemostatic potential of PLTs. All measurements were performed on Days 1 and 5 of storage.
RESULTS: After 5 days of storage at 4°C, only 31 ± 27 percent of P-selectin mRNA and 29 ± 41 percent of glyceraldehyde-3-phosphate dehydrogenase mRNA were lost, while minute amounts of the mRNAs were detectable at 22°C. In PCs stored at 4°C the percentage of P-selectin–positive PLTs was significantly higher when compared to PCs stored at 22°C. Soluble P-selectin concentrations did not significantly differ between both storage temperatures. Thrombelastography revealed significantly shorter reaction times in PLTs kept at 4°C.
CONCLUSION: Our data indicate that storage at 4°C is accompanied by maintained mRNA levels. PLTs with intact mRNA levels and short reaction times in thrombelastography might be functionally superior to PLTs that are devoid of mRNA and show less augmented P-selectin surface expression. In therapeutic applications, that is, if PLTs are transfused to control acute bleeding, PLTs kept at 4°C may be advantageous.     

Ultrastructure of human platelets processed for transfusion under standard blood bank conditions

Platelets processed for transfusion are routinely subjected to centrifugation, mechanical agitation and storage at either room temperature or 4 C. To evaluate morphologic changes associated with standard blood bank conditions, platelet units were grouped into four categories: linear agitation at room temperature, agitation at a 90 degrees arc with a Hemolater at room temperature, agitation at a 360 degrees arc with a commercial platelet agitator, and refirgeration at 4 C without agitation. Cold (4 C) preservation resulted in a surprisingly good preservation of platelet ultrastructure, even at 72 hours of storage. By contrast, harsh linear agitation at room temperature brought about marked alterations in platelet ultrastructure beginning at 24 hours. The Hemolator agitator with 90 degrees arc was associated with good preservation of platelet organelles even at 72 hours, whereas marked degenerative changes were observed at this time in platelets processed with a commercial agitator with a 360 degrees arc. These results indicate that platelets stored at 4 C or processed at room temperature with an agitator with 90 degrees arc show the best preservation of ultrastructure.     

Effects of the addition of second-messenger effectors to platelet concentrates separated from whole-blood donations and stored at 4 degrees C or -80 degrees C

BACKGROUND: Platelet concentrates (PCs) are currently stored at 22 degrees C under continuous agitation. Because of the potential risk of the overgrowth of bacteria in case of contamination, PC shelf life is limited to 5 days. A mixture of second-messenger effectors is being evaluated to determine if it has benefits for cold liquid storage and cryopreservation of platelets. STUDY DESIGN AND METHODS: PCs separated from whole-blood donations by the buffy coat method were randomly assigned (n = 6 each) to be stored for 5 days at 22 degrees C under continuous agitation or at 4 degrees C after treatment with a platelet storage medium (ThromboSol, LifeCell Corp. ). PCs were also cryopreserved with 6-percent DMSO (final concentration) or with ThromboSol plus 2-percent DMSO (final concentration) (TC). After storage, platelets were analyzed by flow cytometry, transmission electron microscopy, and aggregation and perfusion techniques. RESULTS: Cold liquid storage of ThromboSol-treated platelets resulted in a lower binding of coagulation factor Va on the platelet surface than on platelets stored at 22 degrees C. In transmission electron microscopy, a conversion to spherical morphology was seen in the case of cold liquid storage. No difference between ThromboSol-treated platelets stored at 4 degrees C and platelets stored at 22 degrees C was seen in perfusion studies. Cryopreservation in the presence of TC prevented the reduction in glycoprotein Ib and IV expression on platelet surface that is seen in 6-percent DMSO-cryopreserved platelets. Platelets cryopreserved in TC covered, by thrombus, a significantly greater percentage of the perfused surface after the freezing and thawing process. CONCLUSION: ThromboSol-treated PCs separated from whole-blood donations by the buffy coat method, stored at 4 degrees C for 5 days, or cryopreserved in the presence of TC, maintained in vitro functional activity comparable to that achieved by current methods of storage, although discoid morphology was not preserved during cold liquid storage with ThromboSol.     

Prolonged platelet preservation by transient metabolic suppression

BACKGROUND: In this study whether metabolic suppression can be used to preserve platelet (PLT) function during prolonged storage was investigated. STUDY DESIGN AND METHODS: Washed human PLTs were incubated without glucose and with antimycin A to block energy generation. Metabolic suppressed PLTs (MSPs) were stored for 72 hours at different temperatures to find the optimal storage temperature. Controls were incubated with 5 mmol per L glucose and stored at 22 and 4 degrees C. RESULTS: Following metabolic recovery with glucose, MSPs stored at 37, 22, and 4 degrees C showed an increase in basal P-selectin expression (PSE) reaching greater than 40 percent after about 2, 20, and 48 hours; a decrease in thrombin receptor-activating peptide SFLLRN (TRAP)-induced PSE inversely related to the increase in basal PSE; and a decrease in TRAP-induced aggregation reaching less than 30 percent after about 4, 24, and more than 72 hours. When compared with control suspensions, MSPs stored at 4 degrees C better preserved a low basal PSE and in addition showed a better adhesion to surface coated-von Willebrand factor and fibrinogen in a flow chamber. CONCLUSION: Metabolic suppression before storage at 4 degrees C contributes to better preservation of PLT function.     

以海藻糖为添加剂冷藏保存血小板悬液的研究

本研究探讨以海藻糖(trehalose)为添加剂的血小板悬液冷藏保存方法。采用核素标记法检测血小板生存时间,用比浊法测定血小板聚集率,诱导剂为终浓度11.2μmol/L的ADP。采集兔心脏血,按常规方法制备浓缩血小板悬液(PCs),在悬液中加入50mg/ml的海藻糖,37℃水浴4小时后,放于4-8℃冰箱保存,冷藏12天后,测定血小板聚集功能和输入自身体内后的生存时间。结果表明:常温和冷藏储存24小时后的PC血小板聚集率分别为(75.3±9.8)%和(80.5±12.5)%;输入兔体内24、48和72小时时的血小板存活率分别为(78.1±7.9)%、(65.4±6.7)%、(57.5±7.2)%和(5.1±2.5)%、(2.8±2.0)%、(0.9±0.8)%。加入海藻糖的PC冷藏保存12天后,血小板聚集率为(77.8±9.5)%;输入体内24、48和72小时时的血小板存活率分别为(75.7±11.0)%、(67.0±8.5)%、(56.8±8.0)%,与常温保存24小时对照相比,两者相近,P值均>0.05。结论:海藻糖能保护冷藏储存的兔血小板,延长冷藏血小板在体内的生存时间,经海藻糖冷藏储存的兔血小板功能完好。     

Storage of platelet concentrates

The American National Red Cross has initiated a cooperative clinical study designed to evaluate the therapeutic effectiveness of fresh platelets and platelets stored at 4 or 22 C for up to 72 hours. Preliminary results, in confirmation of earlier work, indicate an inverse relationship between platelet count and bleeding time in patients with thrombocytopenia transfused with fresh platelets. Also, the observed rise in platelet count immediately following transfusion of fresh platelets is generally maintained for four to eight hours after which time it declines significantly.     

Metabolic changes during platelet storage

Platelet concentrates (PC) were stored in plastic bags with continuous shaking at 4, 22, and 37 C. Various metabolic parameters were examined over a 72-hour period. At 22 C, the pH and PO2 declined over 72 hours while the PCO2 and lactate increased. Hypotonic shock declined to 70 per cent. This differed from the small amounts of CO2 and lactate found at 4 C and the marked accumulation of metabolites and almost complete loss of shock response at 37 C. Aggregation was always better maintained with 4 C storage. The toxic effect of the accumulation of metabolites on the platelets was tested by adding lactate to fresh PC at zero time. This was effective in lowering the initial pH, markedly inhibiting the response to aggregation and decreasing the total accumulation of lactate during storage, but did not produce an inhibition of hypotonic shock response. The effect of accumulation of toxic metabolites was further investigated by using 72-hour plasma and platelets and recombining each of them with fresh preparations. Platelets were tested under degassed conditions to outline the requirements for oxygen and gasious exchange. Surprisingly, there was less accumulation of lactate and CO2 and better hypotonic shock response. These experiments have detected various changes in viability markers in platelets that are stored under actual blood bank conditions and indicate that the accumulation of lactate is not totally responsible for the toxic inhibition of platelet performance that is found upon storage at 22 C.     

Effect on platelet properties of exposure to temperatures below 20 degrees C for short periods during storage at 20 to 24 degrees C

Background : When platelet concentrates (PCs) are shipped over long distances, it is not always possible to ensure that their temperature is maintained at 20 to 24°C. In addition, PCs are not agitated as during routine storage. Study Design and Methods : Studies have been conducted to evaluate how exposure to temperatures below 20°C in the absence of agitation influences properties of platelets. In initial studies, exposure to 4°C for 3 or 5 hours or to 12°C for 5 or 17 hours on Day 2 of a 5- to 6-day storage period was associated with a loss of discoid shape. This was reflected by slightly lower but statistically different morphology scores after storage compared to those observed with control platelets that were stored only at 20 to 24°C. In addition, a qualitative difference in morphology was noted in controls and PCs held at 16°C for 17 hours. In more detailed studies, both the in vivo viability and in vitro properties of platelets exposed between Day 1 and Day 2 to either 12°C or 16°C for 17 hours were evaluated. The protocol involved a paired study design (n = 4 for each exposure temperature) with the simultaneous storage of two identical PCs, one exposed to 12 or 16°C and the other one maintained at 20 to 24°C throughout the 5-day storage. Results : Exposure to 12°C significantly reduced (p < 0.05 by paired t test) the in vivo recovery to 37.6 ± 13.8 percent (mean ± 1 SD) from 47.8 ± 11.5 percent and the survival time to 2.0 ± 0.3 days from 6.5 ± 1.4 days. On exposure to 16°C, the differences in viability from those of control units were much less but still significant. The in vivo recovery was 42.7 ± 3.8 percent compared to 49.2 ± 3.0 percent and the survival time was 3.5 ± 1.2 days compared to 6.6 ± 0.3 days. The loss of in vivo viability of the test platelets was associated with a loss of discoid shape, as reflected by morphology scores, extent of shape change, and mean platelet volume. In addition, platelet metabolism also appeared to be affected, as suggested by increased lactate production. All of the in vitro properties except for total ATP and residual glucose that were statistically different from those of controls on exposure to 12°C were also significantly different on exposure to 16°C. Conclusion : These findings demonstrate that platelets undergo substantial changes in in vivo viability and in vitro properties when they are exposed to temperatures below 20°C for short periods.