Background
High on-treatment platelet reactivity (HPR) to ADP measured by multiple methods has been linked to adverse post-PCI clinical event occurrence. The correlation of HPR cutoffs is still a matter of debate, since the predictive value and HPR group size are different depending on platelet function assays. To determine the comparable cutpoint, we correlated cutpoints for HPR determined by various assays in the same patient cohort.
Methods
Platelet measures [5µM ADP-induced light transmission aggregation (LTA5μMADP); P2Y12 reaction units by VerifyNow (PRU), and platelet reactivity index by VASP assay (PRI)] were evaluated (n=936 pairs, cohort I) in stable CAD patients during P2Y12 receptor inhibitor treatment. These assays also performed in PCI-treated patients receiving standard aspirin and clopidogrel therapy (n=584, cohort II). The HPR cutpoints were defined as LTA5μMADP >46%, PRU >235, and PRI >50%.
Results
In the stable CAD patients, LTA5μMADP showed significant correlations with PRU and PRI (r ≥0.688). In ROC curve analysis using the cutpoint of LTA5μMADP (>46%), the matched values of PRU and PRI were >234 (AUC 0.943, p<0.001, sensitivity 87.3% and specificity 87.8%) and >60% (Figure A). Among PCI-treated patients, the prevalence of HPR was highest based on PRI >50% (69%) compared with other criteria (≤55%). The comparable values for LTA5μMADP >46% were PRU >235 (AUC 0.850, p<0.001, sensitivity 85.3% and specificity 70.4%) and PRI >59% (Figure B).
Conclusion
The published cutoff values for HPR by LTA5μMADP and PRU were well correlated, whereas published PRI >50% cutoff value may overestimate the risk of HPR. Updated cutoff of PRI > 60% may better stratify the risk for HPR and can be used in future trials.
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