Cold stored platelet concentrates conserve their capability to restore haemostasis despite undergoing phenotypic changes

Introduction Platelet concentrates (PCs) are used to treat or prevent bleeding in patients with impaired platelet function or after injury. These products are currently stored at room temperature (RT) only for 4-5 days due to high risk of bacterial infection. Therefore, cold storage has been investigated as alternative storage temperature to extend the storage time and reduce the risk of bacterial contamination. Therefore, the aim of the study was to analyse the cellular and molecular changes in platelet concentrates stored at RT and 4°C and evaluate their in vitro functionality. Method Apheresis PCs (n=10) were collected from healthy donors and separated into 2 equivalent GMP conforming bags. One PC bag was stored at RT and the other at 4°C, both under agitation. Flow cytometry analysis was performed to determine platelet activation and metabolic status: CD62P, CD63 expression, phosphatidylserine (PS) exposure, mitochondrial membrane depolarization were detected, with and without agonists´ stimulation. Next, aggregometry and thromboelastography (TEG) assays were performed. A novel flow chamber ex vivo system, mimicking the physiological blood flow, was used to assess clot forming ability in a spick-in PCs system. All tests were performed after 1, 6 and 10 days of storage. Results All PCs were valid over the entire storage period at both temperatures according to the quality parameters: platelet count, pH, product weight, and sterility at endpoint. Cold storage maintained slightly higher platelet counts. PCs stored at 4°C displayed enhanced PS exposure, decreased mitochondrial membrane potential and spontaneous degranulation compared to RT-PCs, but did not show lower viability. Nevertheless, the responsiveness of 4°C-PCs, upon TRAP incubation, was not affected. A general time-dependent decrease of platelet responsiveness, at both conditions, was observed during the entire storage period. Moreover, improved aggregation was detected in PCs stored at 4°C upon stimulation with arachidonic acid, ADP, and TRAP-6. While comparable aggregation ability was observed after collagen or ristocetin incubation. TEG showed similar results for both storage temperatures. Finally, in the ex vivo thrombus formation assay all products, at both storage conditions, showed normal thrombus formation, without indication of thrombotic phenotype. Conclusion Our findings indicate that cold storage, despite inducing changes at the molecular level, does not affect the haemostatic functionality of PCs. Therefore, cold storage of PCs might be a promising strategy to extend the storage time, reduce the risk of bacterial infection post transfusion, without either impairing the cell functionality or enhancing the thrombotic risk. Publication History Article published online: 17 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany