Characterization of the in vitro quality parameters of cold-stored platelets containing aggregates.

Background and objectives: Cold-stored platelets (CSP) are being used more widely for the treatment of bleeding because of their longer shelf life. However, storage at low temperatures can induce the formation of platelet aggregates. We aimed to study the impact of aggregate formation on platelet quality and function.

Materials and methods: Apheresis platelets (40% plasma/60% platelet additive solution [PAS-E]) were refrigerated (2-6°C) for 21 days. CSP that developed aggregates (n = 44) were compared with CSP with no aggregates (controls; n = 45). A subset of aggregated CSP (n = 15) was tested before and after being passed through a transfusion administration set containing a 200-μm filter. Donor- and collection-related parameters and in vitro quality parameters were assessed.

Results: Aggregates were identified in 10.9% of CSP, primarily being found following extended storage (median: 16 days). The platelet count was not different between the aggregated (928 ± 158 × 10⁹/L) and control (931 ± 136 × 10⁹/L; p = 0.920) components at day 21. The pH of aggregated components was lower, and the platelets in aggregated components displayed a greater loss of GPIbα, externalization of CD62P and annexin-V, release of extracellular vesicles and degranulation, compared to controls. Functionally, aggregated CSP had potentiated aggregation responses but reduced clot strength (thromboelastography maximum amplitude [TEG MA]) compared to controls. Filtration reduced aggregates in CSP but retained the platelet count and functional properties. Donor-related factors did not correlate with aggregate formation, although certain collection parameters may be implicated.

Conclusion: Platelets within components that contained aggregates were more activated than non-aggregated controls. The propensity for aggregate formation should be considered when selecting a shelf life for CSP.