The release of platelet factor 4 (PF4) from platelets in platelet concentrates (PC) were investigated sequentially in the process of blood collection, and their storage at room temperature for up to 72h with agitation. No appreciable increase in PF4 release was seen immediately after blood collection. However, after resuspension of pelleted platelets with platelet-poor plasma, a significant increase in PF4 release appeared without increase in extracellular lactic dehydrogenase (LDH) concentrations in PC. After storage for 24h, PF4 release was positively correlated with LDH leakage. Approximately 41% of the total amount of PF4 was observed in supernatants in PC after storage for 3 days, while LDH leakage was less than 3% of the total amount in platelets. Rates of pH fall were roughly proportional to the platelet count, and there was positive relationship between PF4 release and the platelet count.
We conclude that storage of platelets under the pelleted condition and resuspension with platelet-poor plasma with the aid of an agitator are critical for better maintenance of PF4 in platelets, and lowering the platelet concentration in the storage bag may prevent release of α-granular constituents in great amounts.