Factors which modulate platelet reactivity as measured by five assay platforms in 3,429 individuals

Background Assessment of platelet function is key in diagnosing bleeding disorders and evaluating anti-platelet drug efficacy. However, there is a prevailing “one-size fits all” approach in the interpretation of measures of platelet reactivity, with arbitrary cut-offs often derived from healthy volunteer responses. Objectives Our aim was to compare well-used platelet reactivity assays. Methods Blood and platelet-rich plasma obtained from the Framingham Heart Study (N=3,429) were assayed using a range of agonists in five platelet assays: light transmission aggregometry (LTA), Optimul aggregometry, Multiplate impedance aggregometry, Total Thrombus-formation Analysis System and flow cytometry. Using linear mixed-effect models, we determined the contribution of pre-analytical and technical factors that modulated platelet reactivity traits. Results A strong intra-assay correlation of platelet traits was seen in all assays, particularly Multiplate velocity (r=0.740; ristocetin vs arachidonic acid [AA]). In contrast, only moderate inter-assay correlations were observed (r=0.375; adenosine diphosphate [ADP] Optimul eMax vs LTA high AUC). As expected, anti-platelet drugs strongly reduced platelet responses with aspirin-use primarily targeting AA-induced aggregation and explained substantial variance (β=-1.735, P=4.59E-780, variance proportion [VP]=46.2%) and P2Y12 antagonists blocking ADP responses (β=-1.612, P=6.75E-27, VP=2.1%). Notably, female sex and older age were associated with enhanced platelet reactivity. Fasting status and deviations from standard venipuncture practices did not alter platelet reactivity significantly. Finally, the agonist batch, phlebotomist, and assay technician (more so for assays which require additional sample manipulation) had a moderate to large effect on measured platelet reactivity. Conclusions Caution must be exercised extrapolating findings between assays and that the use of standard ranges must be medication-specific and sex-specific at a minimum. Researchers should also consider pre-analytical and technical variables when designing experiments and interpreting platelet reactivity measures.