Cold-stored low-titer group O whole blood platelets show progressive basal activation and persistent agonist-inducible responses over 8 days

Low-titer group O whole blood (LTOWB) is increasingly utilized for rapid hemorrhagic resuscitation in severe trauma and critical care settings. While effective, the precise phenotype of platelets within refrigerated LTOWB during storage remains poorly understood. Uncharacterized platelet activation can significantly impact not only hemostatic competence but also contribute to adverse transfusion-related inflammatory and pulmonary responses in critically ill patients. Understanding these dynamics is crucial to optimize LTOWB efficacy and minimize complications.

Researchers assessed platelet surface markers in cold-stored LTOWB units prepared from qualified group O donors, comparing them to apheresis platelet concentrates (APC) and buffy coat-derived platelet concentrates (BC-PC). Units were stored under refrigerated conditions and analyzed at day 0 and day 8. Platelet phenotype was determined by flow cytometry using markers CD41, CD62P, and CD63 under basal conditions and after stimulation with thrombin receptor-activating peptide (TRAP). This design aimed to characterize activation dynamics over typical storage periods.

Compared to APC and BC-PC, LTOWB displayed 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, while basal CD63 in LTOWB was higher than in both comparator products. Over the 8-day storage period, basal CD62P and CD63 levels progressively increased in LTOWB, indicating evolving activation. TRAP stimulation induced marked upregulation of both CD62P and CD63 at both day 0 and day 8. However, stimulated CD63 was lower at day 8 than at day 0, whereas stimulated CD62P remained high, suggesting differential responsiveness.

Cold-stored LTOWB platelets exhibit a distinct and dynamic activation phenotype, characterized by progressive basal activation during storage alongside persistent agonist-inducible responses through day 8.