Validation of a New ELISA-Based Vasodilator-Associated Stimulated Phosphoprotein Phosphorylation Assay to Assess Platelet Reactivity Index in a Chinese Population.

The level of platelet reactivity during P2Y12-adenosine diphosphate receptor antagonist is associated with ischemic and bleeding risks following percutaneous coronary intervention in acute coronary syndrome. Determining platelet reactivity inhibition may be valuable for confirming effective platelet inhibition for individual patients and identifying patients at risk of bleeding. The enzyme-linked immunosorbent assay (ELISA)-based vasodilator-stimulated phosphoprotein (VASP) assay offers unique advantages over other methods and has not been used in the Chinese population. We enrolled 10 healthy volunteers and 54 patients with acute coronary syndrome. The volunteers received no treatment, and patients were administered a loading dose of clopidogrel or ticagrelor. The platelet reactivity index (PRI) was measured using flow cytometry (FC)-VASP and ELISA-VASP at baseline and 8-hour postloading dose. Blood samples of healthy volunteers and clopidogrel- or ticagrelor-treated patients were frozen and stored for 1, 2, and 4 weeks after initial activation. All frozen samples were tested using ELISA-VASP. The PRI assessed by FC-VASP and ELISA-VASP correlated well showing a high degree of consistency in identifying high or low on-treatment platelet reactivity. No significant time-dependent changes in PRI results were observed in frozen samples stored up to 4 weeks compared to nonfrozen samples. The PRI of ticagrelor-treated patients was lower than that of clopidogrel-treated patients. The ELISA-VASP effectively assesses the PRI, and results obtained from frozen specimens are unaffected by storage and shipment prior to assay. Ticagrelor was superior to clopidogrel in decreasing the PRI.