Can aspirin resistance be clinically predicted in stroke patients?

Objectives: Aspirin resistance is one of several possible explanations for limited efficacy or treatment failure of aspirin. However, the predictors of aspirin resistance are not well known. We therefore conducted a study of laboratory-defined aspirin resistance in Korean patients with ischemic stroke and considered a wide range of factors as possible predictors. Patients and methods: A total of 88 patients taking aspirin daily for the secondary prevention of stroke were included. Platelet function was assessed using the Rapid Platelet Function Assay-Aspirin (RPFA-ASA) system and the level of urinary thromboxane B2 (TX-B2). The result of the RPFA-ASA system was expressed as an aspirin reaction unit (ARU). We analyzed a wide range of factors including demographic data, stroke risk factors, and laboratory findings to identify the clinical predictors of aspirin resistance. Results: Eleven (12%) patients were identified as aspirin resistant by the ARU criteria. Univariate analysis showed that an older age, lower LDL cholesterol levels, and concurrent use of angiotensin converting enzyme inhibitors or receptor blockers were related to aspirin resistance by ARU criteria. Aspirin resistance by urinary TX-B2 criteria was observed in 18 (25%) patients and associated with an older age, metabolic syndrome, diabetes, cigarette smoking, and the use of angiotensin-converting enzyme inhibitors or receptor blockers. In multivariate analysis, this association lost significance by ARU criteria, and only lower fibrinogen levels were associated with increased risk by TX-B2 criteria. In addition, the stroke subtypes and the degree of atherosclerosis were not associated with aspirin resistance. The correlation between the two criteria was poor (r = -0.115, p = 0.34). Conclusion: Despite the comprehensive analysis of this study, we failed to identify independent predictors for laboratory-defined aspirin resistance. Additionally, little overlap was found between the two criteria with which to assess aspirin resistance.