(G-267) Comparison of Platelet Quality and Hemostatic Function Across Apheresis Collection Platforms

Introduction:: Platelet products (PLT) are a critical component of hemostatic resuscitation, especially in patients with active bleeding. In the United States (US), PLT can be manufactured in many ways, which include combinations of apheresis collection platforms and resuspension/storage media. Each collection platform implements different flow profiles, residence times, and cell separation approaches, as well as requires unique post-collection product handling techniques. Given the ability of platelets to be activated by shear and surface contact, these differences may have unknown consequences relating to product quality. Previous comparisons between platforms have been largely limited to assessing collection performance or PLT biochemistry. However, there are metrics of platelet functional efficacy not assessed within this scope of comparison. By investigating PLT function through in vitro hemostatic assays, we can gain a larger perspective on how to categorize PLT functionality as well as identify mechanistic differences in collection methodology.

Materials and Methods:: PLT were collected on the three currently used apheresis machines in the US per national blood collection center standards and suspended in either plasma and preservative or platelet additive solution (PAS; an electrolyte solution) and preservative. This resulted in 5 groups: MCS®+ 9000 (Haemonetics; “MCS”) into plasma, Trima Accel® 7 (Terumo; “Trima”) into Isoplate PAS (“TI”) or plasma (“TP”), and Amicus Cell Separator (Fresenius Kabi, “Amicus”) into InterSol PAS (“AI”) or plasma (“AP”). Collections were performed at two distinct geographical sites, with 5 per group per site, allowing for N=10 total collections per group. Collections were set for a standard targeted platelet yield of 3.0x1011 platelets/unit, which was confirmed by a calculated yield post-sampling from platelet count and unit volume. Units were aseptically sampled 1hr post-collection, and cell count, biochemical parameters, hemostatic function, and microparticle (MP) content were measured. A biochemistry panel using an iSTAT Handheld Analyzer consisted of pH, lactate, glucose, sodium (Na+), and potassium (K+). Assessment of hemostatic function was accomplished via light transmission aggregometry (LTA), rotational viscoelastometry (ROTEM) using both EXTEM and FIBTEM agonists, and thrombin generation measured via calibrated automated thrombogram (CAT). MP content was assessed via flow cytometry and reported as the absolute number of CD41+ phosphatidylserine extracellular vesicles between 100-1000 nm in size from 100 µl platelet-poor-plasma aliquots of each PLT unit. Statistical comparisons were made using unpaired t-tests (alpha=0.05).

Results, Conclusions, and Discussions:: Amicus and Trima fluidics are shown in Figure 1, demonstrating significant differences between platforms. Mean calculated yields were 3.0-3.5x1011platelets/unit. Analysis showed elevated glucose in MCS compared to TP(p=0.001) and AP(p=0.001), with no other biochemical differences. Compared to MCS and TP, AP demonstrated decreased aggregometry area under the curve (AUC) when activated with dual agonists, partnered with decreased ROTEM maximum clot formation (MCF). AI had decreased AUC with dual agonists and lower endogenous thrombin potential (ETP) than TI, despite increased MP (Figure 2).
Given the importance of PLT hemostatic capacity when platelets are transfused to prevent bleeding or to treat active bleeding, it is essential we understand how collection methods fundamentally alter PLT function. Simply assessing biochemical metrics of PLT, as was previously done to compare platforms, resulted in limited differences, while we found significant differences across assays which measure in vitro hemostatic function. Across both plasma and PAS groups, PLT collected via Amicus had reduced function when compared to their counterparts collected on MCS or Trima, consistent across assays. The reduced LTA AUCs for PLT collected on Amicus indicates these platelets were less able to aggregate in response to stimulation. This, coupled with decreased MCF and ETP values, implies platelets collected via Amicus may be less likely to activate and form an effective clot at baseline. PLT from Amicus collections were also found to have elevated microparticles. These data indicate it may be the device circuit itself which is causing this functional deficit. Platelets are known to be activated by shear, which can also induce elongation of VWF as well as receptor shedding. Therefore, the fluidics of the Amicus device, which resulted in a 30% increase in AP procedure time compared to TP, and a 22% increase in AI procedure time compared to TI, likely contributed to this effect. This may also explain the observed decrease in hemostatic function in Amicus PLT despite increased microparticles, which are normally associated with increased hemostatic function.
These findings indicate substantial differences between apheresis collection methods and warrant further investigation with future emphasis on how device fluid dynamics impact storage kinetics in platelet products.


Acknowledgements (Optional): :

References (Optional): :