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

Abstract

<h3>Purpose</h3> VerifyNow Aspirin assay (VN) assesses platelet response to ASA, with therapeutic effect defined as ≤ 549 aspirin reaction units (ARU). We aim to evaluate its clinical efficacy in children of all ages, by identifying biochemical resistance (> 549 ARU) and association with clinical thrombosis or bleeding. <h3>Methods</h3> Single-center, observational, analysis of 195 children (< 21 yo) who underwent first VN between 2015-2020 after receiving ≥ 1 enteral ASA dose. Primary outcome was proportion of these patients with ASA biochemical resistance. Secondary outcomes included incidence of new clinical thrombotic and bleeding events in 113 patients receiving ASA monotherapy for ≤ 1 year from VN. Patients receiving concomitant anticoagulation (n=61), dual antiplatelet therapy (n=7), had no follow-up (n=8), or had ASA held (n=6) were excluded from secondary outcome analysis. <h3>Results</h3> Of 195 patients, 56% were male and 53% were Caucasian. At time of VN, median age was 1.8 yrs (IQR 0.08 - 11.9), weight 10 kg (3.5 - 39.1), and BSA 0.47 m² (0.23 - 1.25). Indications for ASA included single ventricle with shunt (36.4%), ischemic stroke (22.6%), Glenn/Fontan (9.7%), vascular disease (7.2%), valvular heart disease (6.7%), VAD (6.2%), coronary disease (2%), RV-PA conduit (3.1%), intracardiac thrombus (2%), ventricular dysfunction (1.5%), and other (2.6%). Median ASA dose before VN was 4.6 (2.6 - 5.8) mg/kg/day; 36% received 1 and 64% ≥ 2 doses. Mean VN was 471 ARU (±66). 14.4% (n=28) had VN > 549 ARU. There were no significant differences in age, weight, BSA, ASA dose, platelet count, hemoglobin, or hematocrit between patients with VN ≤ 549 vs > 549 ARU. Of 113 patients receiving ASA only, mean VN was 471 (±69). Over a median of 252 days (89 - 365), 14 (12.4%) had a thrombotic event after 9 days (3.5-118) and 9 (8%) had a bleeding event after 80 days (25-150) from VN. Mean VN was significantly higher at initial testing in thrombotic (516 ARU, p=0.03) but not bleeding groups (472 ARU, p=0.97). 20% of patients in thrombotic and 33% in bleeding groups had repeat VN performed, with results not significantly different from the group as a whole (482 ARU, p=0.45, and 461 ARU, p=0.39, respectively). <h3>Conclusion</h3> VN platelet function testing identifies biochemical resistance in 14.4% of children. Higher ARU at initial testing may be associated with thrombosis; in contrast, there was no association between ARU and bleeding.