This dissertation, "Prevalence, Profile, Predictors, and Natural History of Aspirin Resistance Measured by the Ultegra Rapid Platelet Function Assay-asa in Patients With Coronary Artery Disease" by Xi, Cheng, 程曦, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Prevalence, Profile, Predictors, and Natural History of Aspirin Resistance Measured by the Ultegra Rapid Platelet Function Assay-ASA in Patients with Coronary Artery Disease Submitted by Cheng Xi for the degree of Master of Philosophy at The University of Hong Kong in October 2005 Background: The efficacy of low-dose aspirin in preventing ischemic complications of atherothrombotic disease is well established. However, previous studies have estimated that 5% to 60% of the population are aspirin-resistant. The profile and predictive factors of aspirin resistance have not yet been fully elucidated. Meanwhile little information exists correlating the laboratory documentation of aspirin resistance with long-term clinical outcomes. Objectives: The purposes of this study were: (1) to investigate the prevalence, profile, and predictors of aspirin resistance using the Ultegra Rapid Platelet Function Assay-ASA; (2) to examine whether aspirin resistance measured by this assay is associated with long-term clinical outcomes. Methods: We prospectively enrolled 472 patients with documented coronary artery disease (CAD) and on aspirin (80-325 mg/day for >= 7 days) but no other antiplatelet agents. We tested aspirin responsiveness by the Ultegra Rapid Platelet Function Assay-ASA (RPFA-ASA; Accumetrics Inc., San Diego, CA). Results are expressed as Aspirin Reaction Unit (ARU). Aspirin resistance was defined as an ARU >= 550, indicating the absence of aspirin-induced platelet dysfunction based on correlation with epinephrine-induced light transmission aggregometry. The primary outcome was the composite endpoint of cardiovascular death, myocardial infarction (MI), stroke, transient ischemic attacks (TIA), or hospitalization for unstable angina (UA). Results: Aspirin resistance was noted in 119 (26.6%) patients with the following characteristics: age 67.59.8 years, female 43.7%, current smoker 11.8%, body mass index (BMI) 25.53.9 kg/m, diabetes mellitus 42.0%, hypertension 74.8%, hypercholesterolemia 70.6%, renal insufficiency 22.7%, prior MI 33.6%, and prescription of