Platelet components with persistent aggregates are more activated, which do not change following pre-transfusion...

Platelet components (PCs) with persistent aggregates are typically discarded. Few studies have characterized components with aggregates. A multicenter study was therefore conducted to determine whether PCs containing aggregates are more activated and whether donor attributes or processing methods influence aggregate formation.

Seven international centers collected and tested apheresis PCs with persistent aggregates (n = 147), and controls without aggregates (n = 65). PCs were assigned a score (0-24), based on the size and number of aggregates. Platelet count, metabolism, activation markers (annexin-V, CD62P, cytokines, glycocalicin and prothrombin F1 + F2 fragments), extracellular vesicles (EVs), and function (collagen aggregation, TRAP-1, and ADP responses) were measured. A subset of PCs was filtered through a transfusion set. Donor attributes and processing methods were also assessed. Data were analyzed using a mixed model of linear regression.

The median aggregate score in PCs with aggregates was 8. PCs with aggregates had a significantly lower glucose concentration, with significantly higher lactate levels. Platelets in PCs with aggregates were more activated, with significantly higher CD62P, annexin-V, and CD61/annexin-V-positive EVs, glycocalicin and prothrombin F1 + F2 fragments compared to controls. Although filtration removed aggregates, the activated platelet phenotype remained unchanged. PCs with aggregates came from older donors with a higher BMI, and from donors who had previously given donations with aggregates.

Platelets in PCs with aggregates are markedly activated, and filtration does not change their phenotype. PCs containing many, large aggregates should be discarded, but those with fewer, small aggregates (aggregate score of 6 or less) could be retained.