Platelet activation in patients with peripheral vascular disease: reproducibility and comparability of platelet markers.

BACKGROUND: Many markers of platelet activation have been described but their reproducibility and comparability in patient populations are poorly defined. OBJECTIVES: We sought to compare markers of platelet and monocyte activation with platelet-monocyte aggregates, a proposed gold standard of in vivo platelet activation, and assess their reproducibility in patients with peripheral arterial disease: a population with substantial platelet activation, inflammation and risk of thrombotic events. PATIENTS/METHODS: Thirty patients with peripheral vascular disease attended on two occasions to permit within-day and between-day comparisons. In vivo platelet and monocyte activation were determined by flow-cytometric quantification of platelet-monocyte aggregation, platelet surface expression of P-selectin and CD40L, platelet-derived microparticles, and monocyte surface expression of CD40 and CD11b. Plasma concentrations of platelet-derived microparticles, soluble P-selectin and CD40L were measured by enzyme-linked immunosorbant assays. RESULTS: Platelet-monocyte aggregation (36.7±7.86%), and platelet surface expression of P-selectin (5.8±1.65%) and CD40L (3.3±1.45%) demonstrated comparable within-day (mean difference±co-efficient of reproducibility; 0.9±15.4%, 0.21±1.65% and 0.2±2.8% respectively) and between-day reproducibility (2.0±12.4%, 0.10±2.25% and 0.9±6.4% respectively). Platelet-monocyte aggregates correlated well with other platelet (r=0.30-0.50, P<0.02) and monocyte (r=0.27-0.47, P<0.03) activation markers. Flow cytometric and assay quantified platelet-derived microparticles showed poorer reproducibility (co-efficient of reproducibility >40). CONCLUSIONS: In patients with peripheral arterial disease, measurements of platelet-monocyte aggregates have good reproducibility and consistently reflect other markers of platelet and monocyte activation.