Aspirin resistance: effect of clinical, biochemical and genetic factors.

Aspirin is one of the cornerstones of treatment for cardiovascular disease. However, some patients may be 'resistant' to its effect: this is associated with adverse cardiovascular outcomes and increased mortality. Measuring response to aspirin is often difficult and there is no accepted definition of aspirin resistance. Many assays are available to test aspirin sensitivity but most are not specific to aspirin and the degree of agreement between different assays is poor. Each assay has its own advantages and disadvantages, and there is currently no one assay that can be recommended for routine clinical practise. There are also many potential modifiers of aspirin response including aspirin dose, non-compliance, disease severity, genetic factors, inflammation, diabetes mellitus, hyperlipidaemia, smoking and interacting drugs. Treating the underlying cause may improve aspirin sensitivity but current data are contradictory with no large clinical trials that have addressed this. Further work is required in this area to determine whether and how aspirin resistance is important clinically, what the best measurement is phenotypically and how this should be used in clinical practise, and whether there are any genetic predisposing factors. This will require well designed prospective studies which take into account the numerous confounding factors that can modify aspirin resistance.