Background: High on-treatment platelet reactivity is an established risk factor for adverse cardiac events in patients taking clopidogrel following percutaneous coronary intervention (PCI).
Methods: Two hundred patients underwent platelet reactivity testing with VerifyNow P2Y12, vasodilator-stimulated phosphoprotein phosphorylation (VASP), and light transmission aggregometry (LTA) with both 5 and 20 μM of adenosine diphosphate (ADP) following PCI. High on-treatment platelet reactivity was defined as a maximum platelet aggregation ≥46% for LTA ADP 5 μM or ≥60% for 20 μM; platelet reactivity index (PRI) ≥50% for VASP; and platelet reactivity units ≥235 for VerifyNow. Correlation between assays was tested using Spearman coefficients (ρ); agreement among tests in regards to high on-treatment platelet reactivity was evaluated with Kappa statistics (κ).
Results: All Spearman correlations had P values <0.001, although ρ ranged from 0.60-0.86. The incidence of high on-treatment platelet reactivity was 39.3% with VASP, 27.3% with VerifyNow, 23.1% with LTA ADP 5 μM, and 16.2% with LTA ADP 20 μM. The strongest correlation was between LTA ADP 5 μM and LTA ADP 20 μM (κ= 0.53, 95% CI 0.37-0.68); the weakest was between VASP and LTA ADP 5 μM (κ= 0.33, 95% CI 0.19-0.47). Overall, the level of agreement between assays was in the moderate to poor range.
Conclusion: Despite evidence that the most commonly used tests are correlated, agreement among tests is modest at best and demonstrates they are not interchangeable.
©2011, Wiley Periodicals, Inc.