Relation between the vasodilator-stimulated phosphoprotein phosphorylation assay and light transmittance aggregometry in East Asian patients after high-dose clopidogrel loading.

OBJECTIVES: We analyzed the relation between platelet aggregation measured by light transmittance aggregometry (LTA) and platelet reactivity index (PRI) measured by vasodilator-stimulated phosphoprotein phosphorylation (VASP-P) assay. BACKGROUND: It has been suggested that LTA and VASP-P assay correlate differently according to the level of P2Y12 receptor blockade by thienopyridines. METHODS: We simultaneously measured platelet function by LTA and VASP-P assay in 466 East Asians undergoing elective percutaneous coronary intervention after a 600-mg clopidogrel loading. High on-clopidogrel platelet reactivity (HPR) was defined by published consensus criteria. RESULTS: The degree of correlation between LTA and the VASP-P assay was different according to PRI levels. The correlation was lower in patients with poor responsiveness (PRI >60%) (n = 216) (0.035 ≤ r(2) ≤ 0.047), which was greater in responsive patients (PRI ≤60%) (n = 250) (0.315 ≤ r(2) ≤ 0.526). Despite a 600-mg loading, East Asians had a high prevalence of HPR (40.1%-63.5%), and the prevalence of HPR also differed between LTA and VASP-P assay. A PRI cutoff of >58% (area under curve, 0.829; 95% confidence intervals, 0.792-0.862; P < .001) corresponded to the published HPR cutoff by 5-µM adenosine diphosphate-induced maximal platelet aggregation >46%. CONCLUSIONS: This is the largest study correlating platelet reactivity measured by LTA and VASP-P assay in a percutaneous coronary intervention-treated cohort. The correlation is dependent on the level of responsiveness. Future investigations are needed to better define the optimal cutoffs of HPR measured by LTA and VASP-P assay for personalized antiplatelet therapy.