A-149 Performance Characteristics of VerifyNow PRU and ARU Tests During a Clinical Method Verification Exercise

Abstract

Abstract Background Dual antiplatelet therapy with aspirin and a platelet P2Y12 receptor antagonist is indicated for the prevention of atherothrombotic events in patients with acute coronary syndromes and for those undergoing percutaneous coronary intervention procedure. Two different assays are available in the VerifyNow Test device for monitoring the anti-platelet therapy response. The aspirin assay (ARU Test) utilizes arachidonic acid as an agonist and is sensitive to acyl salicylic acid. The P2Y12 assay (PRU test) is sensitive to thienopyridines (such as clopidogrel, prasugrel, ticagrelor) and uses adenosine diphosphate (ADP) as an agonist. The PRU test is a non-waived test and ARU test is a waived test. A comprehensive method performance verification is required for the PRU test. We evaluated performance characteristics of the VerifyNow PRU Test and ARU Test for clinical use. Methods The standard precision and accuracy study using two levels (low and high) of quality control materials were performed (N = 10) for both the assays. Alternative qualitative method comparison was carried out (N = 49) using the VerifyNow PRU Test in a reference lab and in-house. The in-house inter-instrument comparisons were carried out (N = 42). The blood samples were obtained from patients taking P2Y12 inhibitors and from normal donors not on any drugs. The results of the PRU Test are expressed in P2YI2 reaction units (PRU). The VerifyNow-Aspirin assay results are expressed as aspirin reaction units (ARU). The statistical analysis to evaluate performance characteristics was carried out using the EP Evaluator. Results The VerifyNow device 1561 precision characteristics for low QC (Obs Mean = 1.5 PRU (N = 10), SD = 0.2; 95% CI for Obs Mean 1.0 to 2.0 PRU) and high QC (Obs Mean = 258.3 PRU (N = 10), SD = 8.2; 95% CI for Obs Mean 252.4 to 264.2 PRU) were within acceptable performance limits. The CV for high QC was 3.2%. The ARU test also demonstrated high precision for two levels (Low QC Obs Mean = 350ARU (N = 10), SD = 0.0); High QC Obs Mean = 583.3 (N = 10), SD = 7.2; 95% CI for Obs Mean = 578.1–588.5) with a CV of 1.2%. The PRU Test Method PRU 1561 In House vs Ref Method Verify Now PRU Test (N = 49) demonstrated overall agreement of 93.9% with positive agreement (intended use population on drugs, N = 27) of 92% and negative agreement (normal non-drug group, N = 22) of 95.8% (Cohen’s Kappa = 87.8%; Kappa >75% indicates “"high” agreement). The McNemar Test for Symmetry passed (P > 0.999, Fisher’s Exact test) in this qualitative method comparison. A value of P < 0.05 would suggest the methods are significantly different. The other in-house instrument 1562 also demonstrated comparable or better performance characteristics. Conclusion It is important to confirm the medical decision limit for the intended use population and determine acceptance criteria while considering biologic variability. However, the reference range verifications with drug responders and non-responders are not always feasible and cost-effective. Based on the qualitative method comparison in this study, we have transferred the medical decision limits from the peer group. The in-house multi-instrument comparison should be repeated every six months to monitor the performance of the instruments.