Dynamics of platelet activation in cold-stored low-titer group O whole blood over 8 days: insights relative to standard platelet concentrates
Low-titer group O whole blood (LTOWB) is increasingly used for hemorrhagic resuscitation in trauma and critical care, but the phenotype of platelets maintained within refrigerated LTOWB remains incompletely characterized. Because platelet activation may influence not only hemostatic competence but also transfusion-related inflammatory and pulmonary responses in critically ill patients, we assessed platelet surface markers in LTOWB in comparison with standard platelet concentrates and examined their evolution during 8 days of cold storage. LTOWB units prepared from qualified group O donors were stored under refrigerated conditions and studied at day 0 and day 8. Platelet phenotype was assessed by flow cytometry using CD41, CD62P, and CD63 under basal conditions and after thrombin receptor-activating peptide (TRAP) stimulation. LTOWB was compared with apheresis platelet concentrates (APC) and buffy coat-derived platelet concentrates (BC-PC). Compared with APC and BC-PC, LTOWB showed a broader distribution of CD41-positive events and a modestly lower median CD41 signal. Basal CD62P in LTOWB was lower than in APC but higher than in BC-PC, whereas basal CD63 in LTOWB was higher than in both comparator products. Between day 0 and day 8, basal CD62P and CD63 increased in LTOWB. TRAP induced marked upregulation of CD62P and CD63 at both time points; stimulated CD63 was lower at day 8 than at day 0, whereas stimulated CD62P remained high. Cold-stored LTOWB displays a distinct platelet activation phenotype characterized by progressive basal activation during refrigerated storage together with persistent agonist-inducible responses through day 8. These findings justify further functional and translational studies integrating platelet, endothelial, and lung-injury readouts to determine whether this storage-associated phenotype has consequences for microvascular hemostasis, immunothrombosis, or transfusion-associated pulmonary complications after hemorrhagic resuscitation.