Immunoassay Determines Response to Low-Dose Aspirin Therapy

A newly available test measures a person's response to low-dose aspirin therapy. The test uses a random urine sample, and is not subject to variables associated with blood sampling.

Low-dose aspirin therapy is routinely prescribed to millions of Americans for cardiovascular disease prevention. The effects of aspirin in reducing blood (platelet) "stickiness" vary considerably from patient to patient. In fact, conservative estimates suggest that aspirin resistance exists in about 25% of the population. Individuals who do not respond to aspirin are more than three times more likely to die from heart disease than those that respond well to aspirin.

Platelets are small blood cells that stick together to form blood clots and control bleeding. They produce a chemical called thromboxane to attract other platelets and increase their stickiness. Aspirin inhibits the production of thromboxane by platelets, therefore reducing their stickiness and limiting the size of clots. The new test, which is called Aspirin Response Testing (ART), measures the level of thromboxane production in apparently healthy individuals.

ART is an enzyme-linked immunoassay (ELISA) that measures the levels of 11-dehydro thromboxane B2 (11dhTxB2) in human urine. It reflects in vivo production of thromboxane A2, which is the target of aspirin therapy. Clinical studies have shown that elevated levels of 11dhTxB2 correlate to increased cardiovascular risk.

Aspirin response is highly assay-specific, meaning that a patient may not test positive for aspirin resistance with tests that stimulate platelet aggregation in vitro via other, less specific pathways. ART is an in vivo test that specifically measures stable thromboxane metabolites. The results are reported in pg of 11dhTxB2 per mg of creatine to standardize results to urine concentration.

SpectraCell Laboratories (Houston, TX, USA) offers ART testing as well as Lipoprotein Particle Profile (LPP) and Functional Intracellular Analysis (FIA) testing. Unlike traditional cholesterol tests, LPP directly measures the number of several classes of lipoprotein particles providing an accurate assessment of cardiovascular risk. The FIA provides an assessment of a patient's nutritional status.

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