Freezing expired platelets does not compromise in vitro quality: An opportunity to maximize inventory potential

BACKGROUND AND OBJECTIVES: Cryopreservation provides an option for long-term storage of platelet concentrates. While platelets are usually frozen as soon as practical after collection (within 2 days), the ability to freeze units at a later stage of the shelf life may improve inventory management. As such, the aim of this study was to determine the impact of freezing platelets approaching expiry (Day 5/6). MATERIALS AND METHODS: Two ABO-matched buffy coat-derived platelets (30% plasma/70% platelet additive solution) were pooled and split to produce matched pairs (n = 8 pairs). Platelets were frozen on Day 1 after collection (cryopreserved platelets [CPPs]) or Day 5 or 6 (expired-CPPs) at -80 degrees C with 5% to 6% dimethyl sulfoxide. In vitro platelet quality was tested before freezing and after thawing and reconstitution in plasma. RESULTS: The majority of prefreeze parameters were equivalent for all platelet units (Day 1 vs. Day 5 or 6). Expired-CPPs had a higher mean postthaw platelet recovery (82 +/- 4%) compared to CPPs (75 +/- 4%; p = 0.0021). Cryopreservation resulted in a loss of surface glycoproteins (glycoprotein (GP) Ibalpha, GPIIb, GPVI), an increase in activation markers (phosphatidylserine and P-selectin) and microparticle release, compared to unfrozen platelets. However, the cryopreservation-induced changes were equivalent in CPPs and expired-CPPs. Functionality was measured by thromboelastography and was similar between expired-CPPs (R-time: 5.3 +/- 0.3) and CPPs (R-time: 5.4 +/- 0.5; p = 0.7094). CONCLUSION: The phenotype and functional profile of platelets frozen at expiry were similar to platelets frozen 1 day following collection. These data suggest that expired platelets may represent a suitable starting material for cryopreservation.