Aspirin does little to prevent blood clots in low-risk women

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Long-term, low-dose aspirin treatment has little effect on the prevention of venous thromboembolism (VTE), or blood clots, in initially healthy women, according to study results published online in the Oct. 16 issue of The Annals of Internal Medicine.

While short-term aspirin therapy can lower the risk for VTE in high-risk patients, the effect of long-term low-dose aspirin in healthy women use remains uncertain. In a secondary analysis of a 10-year randomized trial, Robert Glynn, MD, and colleagues from Brigham and Women's Hospital, Harvard Medical School and Harvard School of Public Health in Boston measured the VTE rates in 39,876 female health professionals, who were randomly assigned to low-dose aspirin or placebo (sugar pill) for 10 years.

Out of the nearly 40,000 female participants, age 45 years or older, 26,779 gave blood samples for testing for mutations that can increase the risk for clot formation.

The researchers randomly assigned each woman 100mg of aspirin every other day or an identical placebo. Every year, they sent each woman a survey about whether they were taking the study pills, side effects of the pills and signs, symptoms and diagnoses of blood clots. If deep venous thrombosis or pulmonary embolism was suspected, a committee of physicians examined the medical records to make sure the diagnosis was correct.

VTE occurred in 482 women during follow-up, higher incidence than that of myocardial infarction and nearly equal to that of stroke. The incidence of VTE was 1.18 among women randomly assigned to active aspirin, compared with 1.25 among women randomly assigned to placebo. For unprovoked VTE, the relative hazard was 0.90.

The researchers reported that aspirin did not affect the frequency of deep venous thrombosis or pulmonary embolism, even in women who had higher rates of blood clots because of gene mutations and other reasons.

The study determined that aspirin does not reduce the risk of blood clots forming in the veins in women with few or no risk factors.