Aspirin response evaluated by the VerifyNow Aspirin System and light transmission aggregometry

Patients with inadequate platelet inhibition by aspirin, referred to as aspirin resistance, might have an increased risk of suffering cardiovascular events. Therefore, identification of these patients by measuring platelet function is of great interest. Our objectives were to evaluate performance parameters of VerifyNow and to determine the agreement between VerifyNow and light transmission aggregometry (LTA) ad modum Born.

We included 21 healthy volunteers and 40 patients with stable coronary artery disease. Duplicate measurements of platelet aggregation were performed using VerifyNow and LTA (arachidonic acid 1.0 mM) in healthy volunteers before aspirin and in all participants on four consecutive days during treatment with non-enteric-coated aspirin 75 mg daily. VerifyNow test results were expressed in Aspirin Reaction Units (ARU) and LTA test results in percent of maximal aggregation. The cut-off for determination of aspirin resistance was > or =550 ARU and > or =20%, respectively.

All participants were compliant, confirmed by complete suppression of serum-thromboxane B(2). VerifyNow was highly repeatable with a coefficient of variance of 0.5% at baseline and 3.0% during aspirin treatment. No individuals were identified as aspirin resistant with VerifyNow, whereas seven (12%) individuals were identified with LTA. ROC analysis using LTA as the gold standard showed poor sensitivity and good specificity with a cut-off at 550 ARU.

VerifyNow was highly repeatable, but further studies are needed to investigate the relevance of the cut-off level at 550 ARU for detecting aspirin resistance.