Determination of Individual Response to Aspirin Therapy Using the Accumetrics Ultegra RPFA-ASA System

The initiation of aspirin (ASA) therapy is recommended in a significant population of patients at risk for cardiovascular disease. The incidence of ASA nonresponsiveness among the population has been reported to range from 5 to 60%. This wide range is due in large part to the lack of standardization of platelet aggregation methods used to determine the extent of response to ASA, many of which require technique-dependent sample preparation or pipetting steps. The Ultegra RPFA-ASA is an easy-to-use whole-blood point-of-care assay that incorporates a single-use cartridge to detect platelet dysfunction resulting from ASA. A cutoff value to demonstrate ASA resistance was established at 550 aspirin response units (ARU). The correlation coefficient (r) calculated from method comparison with epinephrine-induced optical aggregometry is 0.902. The precision of the assay reported with control samples is 3.2 to 5.4% in the responsive range (ARU < 550) and 2.6 to 4.5% in the nonresponsive range (ARU ≥ 550). Intrarun precision determined by NCCLS protocol using whole blood is 2.5%, and total precision is 5.8%. The system was used in a prospective, multicenter study incorporating 422 patients. The reported incidence of ASA nonresponsiveness in this study is 23%.