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Different methodologies for evaluating the effect of clopidogrel on platelet function in high‐risk coronary artery disease patients

Summary.  Background: Two point‐of‐care (POC) systems have been recently proposed as rapid tools with which to evaluate residual platelet reactivity (RPR) in coronary artery disease (CAD) patients. Objectives and Methods: We compared Platelet Function Analyzer‐100 (PFA‐100) closure times (CTs) by collagen/adenosine 5´‐diphosphate (ADP) (C/ADP CT) cartridge and the VerifyNow P2Y12 Assay (VerifyNow) with light transmission aggregation (LTA) induced by 2 and 10 μmol L–1 ADP in 1267 CAD patients on dual antiplatelet therapy who underwent percutaneous coronary intervention. We also performed the vasodilator‐stimulated phosphoprotein (VASP) phosphorylation assay by cytofluorimetric analysis in a subgroup of 115 patients. Results: Cut‐off values for identifying RPR were: ≥ 54% and ≥ 66% for LTA induced by 2 and 10 μmol L–1 ADP respectively, and ≥ 264 P2Y12 Reaction Units (PRU) for VerifyNow. The cut‐off for PFA‐100 C/ADP CT was ≥ 68 s. RPR was detected in 25.1% of patients by 2 μmol L–1 ADP‐induced LTA (ADP‐LTA), in 23.2% by 10 μmol L–1 ADP‐LTA, in 24.4% by PFA‐100, and in 24.7% by VerifyNow. PFA‐100 results did not parallel those obtained with LTA. VerifyNow showed a significant correlation (ρ = 0.62, P < 0.001) and significant agreement (k = 0.34, P < 0.001) with LTA induced by 2 μmol L–1 ADP. The correlation was similar but the agreement was better between VerifyNow and 10 μmol L–1 ADP‐LTA (ρ =  0.64, P < 0.0001; k = 0.43, P < 0.001). Significant relationships were found between VASP platelet reactivity index and both ADP‐LTA and VerifyNow. PFA‐100 C/ADP CT did not significantly correlate with any of the other assays. Conclusions: Our results show a significant correlation between LTA and VerifyNow but not the PFA‐100 C/ADP assay. Clinical validation studies for POC systems are necessary.