Background: Platelets are currently stored at 22°C (room temperature-stored) for clinical purposes. This approach has numerous downsides including limited storage time due to risk of bacterial growth, and increased costs caused by bacterial testing or pathogen reduction. Platelets stored at 4ºC (cold-stored) were the standard of care in the 1960s and 70s, and while they generally perform better than room temperature-stored platelets in in vitro assays, functional studies in vivo have yielded contradictory results.

Methods: Eight healthy human participants were included in the analysis of this randomized, cross-over study. A double unit of apheresis platelets was collected from each subject for autologous transfusion. Platelets were stored for 5 days at either 4ºC, or 22ºC, based on randomization. On day 5, platelets were transfused 12-24 hours after participants received a loading dose of acetylsalicylic acid and clopidogrel. An array of platelet function testing was done at baseline, after loading dose, and after transfusion (1h, 4h, 24h). The first round was followed by a wash-out period of at least 10 days, and a second sequence of collection, antiplatelet loading dose, and transfusion with platelets stored under alternate conditions from the first sequence. The primary endpoint was defined as post-transfusion platelet αIIbβ3 integrin activation in response to agonists for pathways inhibited by dual antiplatelet therapy, measured by the VerifyNOW assay. Secondary endpoints included platelet function testing by bleeding time, VASP-phosphorylation, light transmission aggregometry, and flow cytometric analysis of platelet αIIbβ3 integrin activation and α-granule secretion.

Results: All cold-stored platelet units passed quality control analyses, and no platelet aggregates were observed at the end of the storage period. One room temperature-stored unit had to be discarded due to quality control failure. Transfusion of a double unit with 5 day cold-stored platelets was tolerated well by all recipients. The absolute number of transfused platelets did not differ significantly between the cold-storage arm and the room temperature storage arm. The corrected count increment did not differ significantly at 1h after transfusion, but was significantly lower in the cold-stored group at the 4h, and 24h time points. The primary endpoint, platelet function testing by VerifyNOW, showed reversal of the effect of acetylsalicylic acid with both products at 1h and 4h post transfusion, but platelet inhibition re-appeared after 24h post transfusion in the cold-storage arm, presumably due to accelerated clearance of cold-stored platelets. No significant differences were observed between the two products in the VerifyNOW assay for clopidogrel. The bleeding time (a secondary endpoint) did not differ significantly at any time point between the cold-stored and room temperature-stored transfusion group. However, the bleeding time improved or remained unchanged in all recipients transfused with room temperature-stored platelets, whereas, transfusion of cold-stored platelets caused prolongation of the bleeding time in 50% of recipients. Surprisingly, platelets isolated from recipients of room temperature-stored platelets aggregated significantly better in response to collagen compared to platelets isolated from recipients of cold-stored platelets at 1h and 4h post transfusion. Other secondary endpoints, including VASP-phosphorylation, αIIbβ3 integrin activation and α-granule secretion by flow cytometry, and platelet aggregation in response to arachidonic acid and ADP did not differ significantly between the two treatment groups.

Conclusion: We report the first safety and efficacy data of 5 day cold stored platelets in plasma. Unexpectedly, some endpoints demonstrate agonist- and assay-dependent inferiority of cold-stored platelets at early and late time points. Further studies are needed to determine the maximum storage time, and the efficacy of cold-stored platelets in actively bleeding patients and patients with platelet dysfunction.


No relevant conflicts of interest to declare.

Author notes


Asterisk with author names denotes non-ASH members.

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