Poster P9 - Platelet Products Stored in Plasma or Additive Solution Maintain Function for 21 Days of Cold Storage

Introduction: Platelet products (PLT) are crucial in hemostatic resuscitation of bleeding trauma patients. PLT can be manufactured in different resuspension/storage media (plasma or platelet additive solution (PAS)). Many PLT are discarded after 5-7 days of room temperature (RT) storage. Cold storage (CS) of PLT may extend shelf-life while preserving hemostatic function. Comparisons between collection medium and storage conditions of PLT are limited and could support expanded use of CS-PLT. Assessment of these products in the biochemical and hemostatic sphere of interest is largely limited to clinically available assays in which the product is static during testing. However, given the kinetic mechanisms of hemostasis, static assays may be missing important functional metrics that can only be assessed under physiologically relevant flow profiles. This study utilizes a novel microfluidic device replicating human vasculature under arterial and venous shear conditions, which produces kinetic functional metrics in conjunction with the aforementioned static assays. This interim analysis focuses on the concomitant effect of temperature and storage solution.

Materials and

Methods: PLT were collected via apheresis using the Trima Accel 7 and suspended in either plasma (n=9) or Isoplate PAS (n=9) and preservative. Units were sampled then stored at 4°C (CS) for 21 days or 22°C (RT) for 7 days, with testing on days 0, 7, 14, and 21. Static hemostatic function was measured via light transmission aggregometry (LTA) using dual agonists (ADP and epinephrine (A+E)), ROTEM ExTEM, and thrombin generation. A microfluidic model of hemostatic resuscitation assessed the ability of the stored PLT “donor” to resuscitate healthy "recipient” whole blood (WB, n=3) with an induced coagulopathy of dilution or PLT inhibition (6.4uM ticagrelor) when flowed through a model of vascular injury. Donor and recipient samples were incubated with anti-CD41 antibodies conjugated to different fluorophores and fluorescently imaged via microscopy for 20 minutes or until hemostasis of the injury site is achieved. Surface area (SA) of deposited donor and recipient PLT was measured over time. Groups were compared using unpaired t-tests (alpha=0.05).

Results, Conclusions, and Discussions: Results are expressed as percent change from day 0 to day 7 (RT) or day 21 (CS) (Figure 1). Plasma PLT had a smaller change over storage for each hemostatic parameter compared to their PAS counterparts. CS PLT had a slight loss of function for LTA area under the curve, with a reduction of 73.05% and 66.74% for plasma and PAS respectively, comparable to RT PLT (66.68% and 64.75%). ROTEM clotting time was not significantly different between CS and RT PLT. ROTEM maximum clot firmness in CS PAS PLT was significantly lowered compared to RT (53.74% vs. 18.42%, p< 0.001), but not in plasma. In the microfluidic model (Figure 2), donor PLT were visibly incorporated into clots and PAS and plasma PLT had similar maximum SA deposition at arterial shear (3500/s) in both a dilutional (33010 vs. 51212µm2) and PLT inhibited (32969 vs. 22444µm2) model at day 0.
PLT stored in plasma better preserved hemostatic function compared to PAS, while CS-PLT maintain hemostatic function over 21 days compared to their RT counterparts after 7 days. Extended PLT storage duration with CS-PLT could solve the problem of blood product shortages across the country for patients with bleeding.
Assessment of PLT pre-transfusion has previously been limited to biochemical metrics and cell count. Development of storage mediums like PAS are based on preservation of PLT count throughout storage. However, this data suggests that PLT count is not the best metric for unit quality, and storage mediums intended for maintaining cell count may result in worse functionality. This is further explored through use of flow-based functional testing like microfluidics. Achievement of physiologic hemostasis is reliant on mechanisms of shear stress, impacting pro-coagulant molecules and allowing processes like VWF unfurling and elongation to occur. True PLT function cannot be determined via biochemical markers alone, but rather a cohesive analysis of cell function, plasma content, and mechanistic parameters. Use of microfluidics in parallel with clinical assays may offer the widest lens of hemostatic capacity for individual PLT products and could be used to identify the most effective PLT storage mediums and temperatures for specific clinical scenarios.

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