Clinical Significance of Acute and Serial Platelet Function Testing in Acute Ischemic Stroke

BACKGROUND: We sought to investigate the clinical implications of platelet reactivity to aspirin and the variability in the platelet reactivity to aspirin during acute periods for the risk of vascular events in patients with acute ischemic stroke. METHODS AND RESULTS: This was a single‐center, prospective, observational study. The aspirin reaction unit was blindly measured at the following two times: after 3 hours of aspirin loading and on the fifth day of aspirin administration. High on‐aspirin platelet reactivity (HAPR) was defined as an aspirin reaction unit ≥550 IU. The primary outcome measure was the 1‐year composite of stroke, myocardial infarction, and vascular death. A total of 805 patients (aged 66±12 years, 61% male) were analyzed in this study. Ninety‐nine of 805 (12.3%) patients and 78 of 558 (14.0%) patients had HAPR at the time of the fifth day of aspirin administration and after 3 hours of aspirin loading measurements, respectively. Patients with HAPR than normal on‐aspirin platelet reactivity at the fifth day of aspirin administration measurement were more likely to have experienced 1‐year vascular event. HAPR at the fifth day of aspirin administration measurement was independently associated with a greater risk of experiencing 1‐year vascular event (hazard ratio, 1.84; 95% confidence interval, 1.07–3.19). Moreover, persistently HAPR substantially increased the risk of 1‐year vascular events (hazard ratio, 3.11; 95% confidence interval, 1.23–7.86). CONCLUSIONS: These results suggest that HAPR during the acute stage of ischemic stroke increases the risk of subsequent vascular events and that serial aspirin reaction unit measurements may identify patients with acute ischemic stroke who are at a higher risk for vascular events. Additional studies are warranted to determine the appropriate treatments for patients with acute ischemic stroke with HAPR.