Comparison of the VASP assay and platelet aggregometry in the evaluation of platelet P2Y12 receptor blockade

INTRODUCTION It has been shown that incomplete blockade of platelet reactivity is a risk factor for future ischemic events in patients with cardiovascular diseases. Despite these findings, there is yet no gold standard of platelet reactivity estimation. The 2 most commonly used methods in platelet testing are platelet aggregometry and vasodilator-stimulated phosphoprotein phosphorylation (VASP) assay. They both showed the predictive value for future adverse events in cardiac patients; however, there are few data that compare these 2 methods. OBJECTIVES The aim of the study was to compare the results of aggregometry (multi-electrode aggregometer [MEA]) and flow cytometric VASP assay used to determine platelet reactivity after the administration of P2Y(12) receptor blockers. PATIENTS AND METHODS The study included 17 healthy volunteers (12 men, 5 women; aged 41 +/- 10 years) and 12 patients (men, aged 62 +/- 12 years) with stable coronary artery disease treated with elective percutaneous coronary inter-vention with stent implantation. In volunteers, the blood was collected and tests were performed before and after 10-minute incubation with 5 nmol/l of cangrelol. In patients, the blood was collected for measurements before and after ingestion of 300 mg of clopidogrel. Aggregometry measurements included adenosine-diphosphate (ADP)-induced maximal aggregation (A(max)) and ADP-induced area under the aggregation curve (AUC). The platelet reactivity index (PRI) was determined using the VASP assay. RESULTS The use of cangrelor and clopidogrel was associated with a significant inhibition of platelet reactivity measured using the above methods. In both groups, the degree of inhibition was significantly greater when measured with the aggregation method compared with the VASP assay. The only significant coefficient of correlation between the VASP assay and aggregation results was observed in volunteers after platelet incubation with cangrelor (r= 0.81 between PRI and A(max), r = 0.68 between PRI and AUC). CONCLUSIONS Compared with the VASP assay, ADP-induced platelet aggregation shows a greater ability to detect a decrease in platelet aggregation after P2Y12 antagonists. These tests are not inter-changeable because they measure different aspects of the P2Y12 receptor blockade.