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Warming Up to Cold-stored Platelets.

Platelets are critical in stopping hemorrhage as they treat the underlying coagulopathy and improve patient outcomes. However, maintaining an adequate platelet supply is challenging, particularly in austere settings. Thus, additional products such as coldstored platelets are needed. In this issue, Strandenes et al. describe the completion of a pilot trial that demonstrates the feasibility of conducting a larger randomized controlled trial to assess the safety and efficacy of cold-stored compared to room temperature (standard) platelets in patients undergoing complex cardiothoracic surgery. This pilot trial has an unusual twostage design. In stage I, 50 adult patients undergoing complex cardiac surgery at high risk of hemorrhage were randomized to receive either cold-stored (n = 25) or standard (n = 25) platelets. Both products were agitated (as standard with room temperature platelets but not required to preserve function in cold-stored platelets) and were stored up to 7 days. Patients were transfused based on the clinical judgement of the surgeon and/or anesthesiologist, who remained blinded. Stage II was a single-arm prospective observational study where an additional 15 patients were transfused with up to 2 cold-stored platelet units without agitiation stored for 8 to 14 days. If additional platelets were needed, patients received standard platelets. Platelet availability is hindered by the need for bacterial screening and the product’s short shelf-life. Unlike red blood cells and plasma, which are stored refrigerated and/ or frozen, platelets are stored at room temperature where bacteria can grow, potentially causing septic transfusion reactions. To decrease this risk, platelet shelf-life is limited to 5 or 7 days depending on product testing (often resulting in hospital availability for less than 3 days and high product wastage). In addition, the Food and Drug Administration and other regulatory agencies have recommended mitigation steps, including pathogen inactivation and bacterial screening. There is concern that implementation of the new Food and Drug Administration guidance could decrease the availability of platelets for transfusion in the United States; this decrease in availability could put patients at risk. To overcome these problems, alternative products are needed. These alternatives include lyophilized platelets and cryopreserved platelets in addition to cold-stored platelets. All three products have potential to mitigate septic reactions and extend product shelf-life and are in clinical trials. Lyophilized and cryopreserved platelets are in earlier-phase clinical trials than cold-stored platelets but have extended shelf-life of years rather than days, potentially diminishing the future need for cold-stored platelets. Cold-stored platelets are not new. Platelets were coldstored until a study showed that they had increased clearance and reduced survival in vivo compared to standard platelets. Since the main indication for a platelet transfusion is to prevent bleeding in thrombocytopenic hematology patients, the reduced half-life of cold-stored platelets was seen as a significant detriment. However, for bleeding patients, especially trauma patients, the platelets need to be transfused early in resuscitation and do not need extended posttransfusion survival. Literature from in vitro and preclinical studies demonstrated that cold-stored platelets might be an attractive alternative for therapeutic versus prophylactic indications. When platelets are exposed to the cold, they undergo morphologic and molecular changes that create a hemostatically primed state. Cold-stored platelets also maintain shearand agonist-induced aggregation responses, display