Aspirin resistance: truth or dare.

Acetylsalicylic acid, or aspirin (ASA), is widely used in patients with cardiovascular disease to prevent acute ischemic events. However, platelet response to ASA is not equal in all individuals, and a high variability in the prevalence of ASA resistance is reported in the literature (0.4-83%). Actually, ASA resistance is poorly understood; this stems from the fact that its definition is unclear, its presence can be evaluated by a number of assays that are not equivalent, and its prevalence may vary widely based on the population studied. This article (1) exposes the difficulties in defining ASA resistance; (2) discusses the mechanisms by which ASA resistance may occur; (3) presents the characteristics that may put patients at greater risk of exhibiting ASA resistance; and (4) discusses the clinical impact of ASA resistance in patients requiring chronic therapy.