Blood Markers Might Predict Clotting Risk With HRT

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On the flip side, lower levels of anti-coagulant proteins, or proteins which are natural blood thinners, also increased the risk of clotting. Lower levels of protein C were linked with double the risk, lower protein S with triple the risk, and lower levels of antithrombin were associated with a 1.7-fold increased risk.

The most important factor turned out to be elevated D-dimer, which is present in 25 percent of women and which increased the risk of thrombosis in women receiving HRT sixfold.

"That gets in the range of 1 percent of women a year, so that's pretty significant clinically," Cushman said. "You might think a little harder if you want to take hormones, or take them for a minimal amount of time."

Not everyone considering HRT needs to get their D-dimer tested, however.

"The bottom line is that for some women who are concerned and their doctor wants to do something to try to help determine risk, D-dimer might be warranted," Cushman said. The test for D-dimer is available commercially.

"The study is provocative, but I can't see it as going to the bedside for patients when deciding who goes on HRT," said Dr. Steven Deitelzweig, system department chair of hospital medicine and vice president of medical affairs at Ochsner Health Systems, in New Orleans. "These are pretty unusual markers. There might be some implications for people with a personal or family history. For a select group, it gives vascular experts additional tools to bring to the benefit of patients."

And Cushman noted these blood markers do not tell the whole story.

"There's not one single thing that causes venous thrombosis. You might live life with higher D-dimer and never get a blood clot because the circumstances just aren't right," Cushman said. "But we know from previous work that obesity enhances the risk with hormones so if you were obese and thinking about taking hormones and your D-dimer was high, these things all add together. The context has to be considered in decision-making. For any individual person, her doctor needs to review all of her risk factors when considering taking hormones."

More information

Visit the National Heart, Lung, and Blood Institute for more on the Women's Health Initiative.