(P-CB-14) Preliminary Comparison of the Hemostatic Properties of Cold-Stored Apheresis Platelets and Platelets Stored in Whole Blood

Transfusions of cold-stored platelets (CSPs) and whole blood (WB) are increasingly used to treat traumatic injury while easing logistics and improving blood availability. Although both CSPs and WB are indicated for resuscitation, it is unclear how hemostatic function differs between the two product types. Whereas the effect of refrigeration on platelets is well-characterized, the effect of storing platelets in the presence of other components in WB has received less attention. Here, CSPs and WB were collected from the same donors and compared for in vitro quality and platelet function during 21 days (D) of cold storage.

Study

Design/Methods:

A total of 8 consented donors provided both 1 unit of apheresis platelets and 1 unit of WB on 2 separate dates. CSPs were collected on the Trima Accel and stored in plasma. WB was collected in CPD and leukoreduced with a platelet-sparing filter. A sample was taken on the day of collection prior to storage at 2-6°C. Units were sampled on D2, 7, 14, and 21 of storage. Hematological and metabolic parameters were measured on unprocessed samples. To evaluate platelet function, WB was processed to platelet-rich plasma. Platelets were assessed by flow cytometry (CD42b, CD62P, Annexin V) and light transmission aggregometry (LTA). Clot formation and retraction were measured using a novel microplate assay. Statistical testing was conducted by mixed-effects analysis with a threshold of p< 0.05. Product types were compared by day using Sidak’s multiple comparisons test.

Results/Findings:

Percent loss of platelets during storage was not significantly different between CSPs and WB except at D14 (CSPs, 71 ±6%; WB, 55 ±8%, p<sub>adj = 0.03). The pH was significantly lower in WB than CSPs but remained >6.5 for all units. Neither glucose nor lactate levels differed between product types. The percentage of CD62P⁺ platelets trended higher for platelets stored in WB (WBPs) and was significantly increased compared to CSPs on D21 (CSPs, 46% ±9%; WBPs, 72 ±13%; p<sub>adj = 0.03). Product type had no effect on expression of CD42b or annexin V staining. Maximum aggregation in response to collagen and ADP was significantly lower in WBPs than CSPs on D2, D7, and D14 but there was no significant difference on D21. Visual inspection of retraction curves suggested that by D7 cold storage affected time to maximum clot density and inhibited clot retraction.

Conclusions:

Despite vastly different storage microenvironments and absolute platelet concentrations, quality parameters were similar between CSPs and WB. WBPs appeared to lose hemostatic activity more rapidly than CSPs; however, caution should be used when interpreting platelet functional assays for CSPs and WBPs. Variables like platelet concentration and WB hemolysis could confound results obtained by current methods. Further work is needed to develop assays that are compatible with stored WB versus a concentrated component.