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Post-Op Blood Clot Risk High

Study Finds Postoperative Blood Clot Risk Greater, More Persistent Than Experts Thought
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WebMD Health News

Dec. 4, 2009 -- The risk of getting a potentially deadly blood clot after surgery is even higher than experts believed -- and it persists longer than they thought, according to a new study that evaluated nearly a million women in the U.K., including nearly 240,000 who had surgery.

''We already know there is a substantially increased risk of blood clots after major surgery," says researcher Jane Green, MD, PhD, a clinical epidemiologist at the University of Oxford, England. "What is striking about our finding is the scale of the risk. Even more important is the fact that this risk is raised for quite a long time."

"The bulk of the increased risk is up to three months after surgery," she says. "The peak is at three weeks. Then the risk falls off." But some level of risk remains for a year, the researchers say.

The study is published in BMJ Online First.

Blood Clot Risk After Surgery: Study Details

Green's team drew on questionnaire data from the Million Women Study, which recruited 1.3 million women, average age 56, through the National Health Service to quiz them about lifestyle and other characteristics for health research.

For this study, they looked at hospital admission and death records for 947,454 participants, tracking each for an average of 6.2 years.

They tracked women who were diagnosed with venous thromboembolism, an umbrella term for both deep vein thrombosis (a clot in a vein deep within the body) and a pulmonary embolism (blockage of the main artery of the lung). The risk of blood clots is known to be higher after surgery, especially orthopedic surgery, but less is known about long-term risk and about patterns with different surgeries.

Green and her colleagues compared the risk of blood clots for those who didn't have surgery with those who did have surgery. Of the total, 239,614 women had surgery during the follow-up period; 5,419 of those were admitted to the hospital for blood clots, and 270 died of a blood clot.

The researchers excluded from the analysis women who had been in the hospital previously for blood clots or who had a history of blood clot problems, as well as those who had a cancer history or who had surgery the year before the follow-up started.

Blood Clot Risk After Surgery: Study Results

Compared to the risk of women who didn't have surgery, those who had surgery in the hospital were nearly 70 times more likely to be admitted with blood clots during the first six postoperative weeks. Women who had day surgery (including arthroscopy and minor procedures such as biopsies) were nearly 10 times as likely to have a clot as those who had no surgery.

Overall, one in 140 middle-aged women in the U.K. who have surgery in a hospital would be expected to be admitted with a blood clot during the 12 weeks after the surgery.

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