Prevalence of nonresponsiveness to aspirin in patients with symptomatic peripheral arterial disease using true point of care testing.

Purpose: This study was designed to determine the prevalence of platelet nonresponsiveness to aspirin using point of care testing in a population with symptomatic peripheral arterial disease (PAD).
Methods: This was an observational, single-centre study including all patients with symptomatic PAD receiving aspirin. In patients receiving dual antiplatelet therapy with additional clopidogrel, platelet responsiveness to clopidogrel also was tested. Platelet responsiveness was assessed with the VerifyNow P2Y12 assay. Patients with residual aspirin reaction units ≥550 and platelet reactivity units ≥234 were considered nonresponders. The study's primary endpoint was to determine the prevalence of nonresponsiveness to aspirin; secondary endpoints included the prevalence of dual nonresponsiveness.
Results: In total, 145 consecutive patients (mean age 67 ± 9 years) receiving aspirin 100 mg were tested, whereas 128 of 145 (88.3 %) were under dual antiplatelet therapy with additional clopidogrel 75 mg. The prevalence of nonresponsiveness to aspirin was 20.7 % (30/145). Among the 128 patients receiving dual antiplatelet therapy, 65 (50.8 %) demonstrated nonresponsiveness to clopidogrel and 16 (11.7 %) dual nonresponsiveness to both aspirin and clopidogrel. Aspirin nonresponsiveness was not significantly different in patients suffering from diabetes, renal disease, critical limb ischemia (CLI) or those receiving statin, antihypertensive or proton-pump inhibitors therapy. Clopidogrel nonresponsiveness was significantly higher in older patients (p = 0.01) and those suffering from CLI (p = 0.03) and renal disease (p = 0.001) and significantly lower in smokers (p = 0.01).
Conclusions: The prevalence of platelet nonresponsiveness to aspirin detected using the VerifyNow point of care testing in symptomatic PAD patients was 20.7 % and the clinical impact of the phenomenon merits further investigation.