Impact of Test Conditions on ADP-Induced Platelet Function Results With the Multiplate Assay: Is Further Standardization Required?

BACKGROUND: Platelet function testing was suggested to help tailor P2Y12-inhibitor therapy; however, the lack of proper standardization is still a limitation. METHODS: In a prospective study, we enrolled clopidogrel-treated and P2Y12-inhibitor naive patients to investigate the influence of (1) time from blood collection, (2) stability of the stored Adenosine diphosphate (ADP) reagent, and (3) the use of enoxaparin on results of the Multiplate assay. Measurements were performed from samples kept for 0, 30, 60, 120, and 240 minutes at room temperature before processing. To determine the impact of the reagent stability, freshly thawed ADP was compared with ADP kept for 3 to 5 or 8 to 13 days at 2 degrees C to 8 degrees C. Finally, samples containing enoxaparin at therapeutic or prophylactic doses were compared with enoxaparin-free blood. RESULTS: A total of 180 measurements were performed. ADP-stimulated platelet reactivity values decreased significantly over time (67 +/- 40 U to 68 +/- 37 U to 58 +/- 37 U to 45 +/- 33 U to 35 +/- 33 U; P < .0001). Consequently, a dramatic reduction was observed in the proportion of patients with high platelet reactivity ( P < .0001). A significant drop in platelet reactivity was observed with ADP stored for 8 to 13 days as compared to freshly thawed ADP ( P = .011). Enoxaparin triggered a slight, concentration-dependent increase in platelet reactivity ( P < .05). CONCLUSION: Test conditions may have profound impacts on the obtained results with the Multiplate assay. Our findings highlight the large influence of the time from sample collection until testing, suggesting that measurements should be performed within an hour of blood collection