Analysis of Platelet Function Testing in Children Receiving Aspirin for Antiplatelet Effects

Aspirin (ASA) remains the most common antiplatelet agent used in children. VerifyNow Aspirin Test® (VN) assesses platelet response to ASA, with therapeutic effect defined by the manufacturer as ≤ 549 aspirin reaction units (ARU). Single-center, observational, analysis of 195 children (< 18 years-old) who underwent first VN between 2015 and 2020. Primary outcome was proportion of patients with ASA biochemical resistance (> 549 ARU). Secondary outcomes included incidence of new clinical thrombotic and bleeding events during ≤ 6 months from VN in those who received ASA monotherapy (n = 113). Median age was 1.8 years. Common indications for ASA included cardiac anomalies or dysfunction (74.8%) and ischemic stroke (22.6%). Median ASA dose before VN was 4.6 mg/kg/day. Mean VN was 471 ARU. ASA biochemical resistance was detected in 14.4% (n = 28). Of 113 patients receiving ASA monotherapy, 14 (12.4%) had a thrombotic event and 2 (1.8%) had a bleeding event. Mean VN was significantly higher at initial testing in patients experiencing thrombotic event compared to those without thrombosis (516 vs 465 ARU, [95% CI: 9.8, 92.2], p = 0.02). Multivariable analysis identified initial VN ASA result ≥ 500 ARU at initial testing as the only significant independent risk factor for thrombosis (p < 0.01). VN testing identifies ASA biochemical resistance in 14.4% of children. VN ASA ≥ 500 ARU rather than ≥ 550 ARU at initial testing was independently associated with increased odds of thrombosis. Designated cut-off of 550 ARU for detecting platelet dysfunction by ASA may need reconsideration in children.