In vitro storage characteristics of platelet concentrates suspended in 70% SSP+™ additive solution versus plasma over a 14-day storage period

Background and Objectives The non-paired two-arm study compared the in vitro storage characteristics of platelets suspended as concentrates in either 100% plasma or a mixture of additive solution (SSP+(TM), MacoPharma, Mouveaux, France) and autologous plasma in a 70: 30 ratio over a 14-day storage period. Materials and Methods The buffy coat-derived pooled platelet concentrates were sampled on days 1, 2, 3, 6, 8, 10 and 14 and tests performed to determine platelet morphology, function, metabolism, activation and apoptosis-like activity. Results Swirling remained strong (score = 3) in SSP+(TM), whilst scores of 1 and 0 were noted for plasma units by end of storage. In contrast to units in plasma, pH levels remained above seven in SSP+(TM) units, increasing after day 10. Percent positive expression of CD62P was similar in both groups on day 1 (median of 54% and 56% for plasma (n = 13) and SSP+(TM) (n = 12), respectively), with SSP+(TM) units showing a more moderate increase in activation after day 10. A progressive decrease in mitochondrial membrane potential was evident in both groups from day 1, whilst annexin V binding was relatively stable from days 1 to 3, with median values remaining below 6%. Subsequent to this, the percentage of platelets binding annexin V increased to approximately 30% by day 14. Conclusion Platelets suspended in a medium of 70:30 SSP+(TM) to plasma ratio performed at least as well as platelets in 100% autologous plasma for up to 10 days of storage. Further, results are suggestive of an apoptosis-like process being involved in the platelet storage lesion.