In vitro evaluation of prestorage pools consisting of mixed A and O platelet concentrates

BACKGROUND: Current FDA regulations allow the prestorage pooling of whole blood-derived platelet concentrates (PCs) of identical ABO type in a recently cleared platelet (PLT) pooling bag (Acrodose, Pall Medical). It is unclear how ABO-mixed PC pools would store if pooled before storage. STUDY DESIGN AND METHODS: Pools consisting of ABO-identical PLTs and mixed A and O PLTs in varying proportions were evaluated on Days 1, 5, and 7 of storage with measures of the PLT storage lesion, lymphocyte activation, and activation of the complement and coagulation system. Data were analyzed by analysis of variance. RESULTS: Pools did not differ on Day 7 in pH (p = 0.63), hypotonic shock response (p = 0.25), extent of shape change (p = 0.26), morphology score (p = 0.18), or white cell count (p = 0.79), but surface P-selectin expression was more evident in the ABO-mixed pools (p = 0.02). Small microscopic clumps of PLTs were observed in all pools, but were more prominent in the ABO-mixed pools (p < 0.01). PLT counts, however, did not differ between pools (p = 0.93), indicating that only a small proportion of PLTs were clumped. Surface A-antigen expression was proportional to the number of A PCs in each pool and did not vary between study days. Anti-A(1) titers were either unchanged or decreased by one dilution. Complement and coagulation activation markers did not differ between pools. CONCLUSION: Pooling A and O PCs is associated with evidence of increased microscopic PLT clumping and activation, but these differences are not exacerbated with 7-day storage. Other major measures of PLT quality do not differ, and there was no evidence of a mixed lymphocyte reaction.