An Examination of Some Factors which Influence the Stability of in Vitro Platelet Responses

Platelet sensitivity to ADP and adrenaline was determined after storage of platelet-rich plasma (PRP) under various conditions to establish those yielding optimal platelet stability. The effects of the exclusion of air from the storage syringes, temperature, PRP dilution and duration of storage were tested. Storage at room temperature (22° C) in the absence of air stabilised PRP pH over 24 h and stabilised platelet sensitivity to ADP up to 4 h. Storage at 4°C and 13 C caused platelet activation and eventually spontaneous aggregation, as evidenced by significant reductions in platelet counts. Samples stored at 37° C were less responsive to ADP and adrenaline than samples maintained at 22 C. Platelet count adjustment to 200 × 10(9)/L reduced platelet sensitivity as reflected by increased agonist EC(50) values and threshold concentrations. Positive correlations between agonist EC(50) values (and between threshold concentrations) for diluted and undiluted samples were obtained, indicating that platelet count adjustment did not affect the ranking order of platelet sensitivity within the subject group. No correlations between platelet count and indices of platelet sensitivity were seen suggesting that differences in platelet aggregation arise from intrinsic differences in platelet sensitivity rather than differences in platelet count. With time of storage the responses to ADP (EC(50) and threshold concentration) and adrenaline (EC(50)) declined to a greater extent for undiluted PRP than for diluted PRP. No changes in the platelet-poor plasma concentrations of the dense granular component, serotonin, occurred in diluted or undiluted samples over 24 h. We conclude that in order to ensure optimal stability of platelets, PRP should be stored at room temperature (22°C) in the absence of air and tested within 4 h of preparation. A decision on platelet count adjustment is also required dependent upon the experimental objectives.