Abstract 17082: Hematocrit Significantly Affects the Results of the Verifynow Assay in Patients Receiving Dual Antiplatelet Therapy
Background: A number of assays have evolved to assess platelet reactivity and identify patients on dual antiplatelet therapy who remain at risk of thrombotic events. The goal of this study was to assess how a number of these assays are affected by clinical and hematological factors.
Methods: We prospectively recruited patients with known vascular disease or risk factors presenting for coronary catheterization and assessed platelet reactivity at baseline and after clopidogrel loading using the VerifyNow P2Y12 assay, Platelet Function Analyzer (PFA-100):Collagen/Epinephrine(Col/Epi), PFA-100:Collagen/ADP(Col/ADP), and platelet aggregometry with 5μ M, 10μ M and 20μ M ADP agonists. Univariate and multivariate regression models were developed to identify clinical and laboratory factors affecting the assays.
Results: Of 198 patients who entered the study 79 patients were excluded due to intraprocedural use of GPIIb/IIIa antagonists or lack of repeat blood sample. Fifty-five patients underwent coronary intervention. Plasma vonWillebrand factor antigen (vWFAg) levels were a significant univariate predictor of PFA-100:Col/Epi (p=0.002) but not Col/ADP closure times. VerifyNow base and platelet reactivity results (PRU) both prior to and after clopidogrel load had a strong negative correlation with hematocrit (p<0.0001, p=0.0004) as did impedance and light aggregometry. Hematocrit remained the only strong predictor of post-Clopidogrel VerifyNow result in multivariate analysis modeling (p=0.001).
Conclusions: Plasma vWFAg levels significantly affect the PFA-100:Col/Epi assay. In contrast to prior small validation studies, performed in normal individuals, we found hematocrit level to have a strong negative correlation with VerifyNow results in this cohort of patients. It is unclear whether the observed correlation is due to truly increased in vivo platelet reactivity in anemic patients or an in vitro phenomenon inherent to the VerifyNow system.
- © 2011 by American Heart Association, Inc.