Estrogen ups blood clot risk for some women

Last Updated: 2006-04-10 16:00:48 -0400 (Reuters Health)

NEW YORK (Reuters Health) - Estrogen therapy is associated with an elevated risk of developing a blood clot in a vein (venous thrombosis) in postmenopausal women who have undergone hysterectomy, according to a new report.

"Our data suggests that although the absolute incidence is relatively low, the use of conjugated equine estrogen increases the relative risk of venous thrombosis in postmenopausal women without a uterus," investigators conclude.

"Women with appropriate indications, such as short-term treatment of severe menopausal symptoms, should use conjugated equine estrogen only after careful consideration of the relative risks and benefits, especially if the women have other risk factors for venous thrombosis, including previous venous thrombosis, older age, obesity, and perhaps factor V Leiden," they advise.

The current findings, which stem from the large Women's Health Initiative trial, are not the first to link hormone therapy with venous thrombosis, but prior supporting data has come from observational studies or from studies that only looked at the effect of combined estrogen/progestin therapy, not estrogen alone.

Dr. J. David Curb, from the University of Hawaii in Honolulu, and colleagues analyzed data from nearly 10,739 women who participated in the WHI estrogen trial. The subjects, who were between 50 and 79 years of age, had undergone hysterectomy in the past and were randomized to receive estrogen or placebo.

During an average follow up of 7 years, more women in the estrogen group than in the placebo group developed a blood clot in a vein (111 women versus 86 women), according to a report published Monday in the Archives of Internal Medicine.

The same was true for so-called deep vein thrombosis -- most often clots in large veins in the legs. Eighty-five estrogen-treated women developed this type of blood clot compared with only 59 placebo-treated women.

The investigators found that the risk of venous thrombosis was highest in the first two years after starting estrogen therapy.

Still, the clotting risk with estrogen-only therapy did not seem to be as high as with estrogen/progestin combination therapy, based on a comparison with previous WHI findings, they point out.

SOURCE: Archives of Internal Medicine, April 10, 2006.