Estrogen ups blood clot risk for some women

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.