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THURSDAY, March 11 (HealthDayNews) -- People suffering from inflammatory bowel disease (IBD) face a greatly increased risk of developing blood clots in their veins, new research discloses.

Most experts, however, are not surprised that the clots, called venous thromboembolisms, are linked to the intestinal disorder. The finding, which show those with IBD have more than triple the risk for clots, will appear in the April issue of Gut.

"The existence of an increased risk of venous thromboembolism in inflammatory bowel disease has been known for at least 30 or 40 years," says Dr. David Clain, associate chief of the division of gastroenterology and liver diseases at Beth Israel Medical Center in New York City. "This is nothing new."

In fact, Clain says, he saw the association in a patient for the first time in 1970, although he had read about it before that.

The findings may, however, validate this knowledge, adds Dr. James Smith, section head of gasteroenterology and hepatology at the Ochsner Clinic Foundation in New Orleans. Smith stresses the absolute number of people with IBD who will develop a blood clot is still very low.

The researchers did manage to isolate the phenomenon to people only with IBD as opposed to other chronic inflammatory or bowel disorders such as rheumatoid arthritis or celiac disease.

The study authors report that previous data on IBD and blood clots was conflicting, with prevalence estimates ranging from 1.2 percent to 6.7 percent in clinical studies and 39 percent in postmortem studies.

IBD is a chronic disease caused by inflammation of the intestines. There are two main types: ulcerative colitis, which is when the large intestine develops ulcers, and Crohn's disease, which refers to an inflammation of the lining and wall of the large and/or small intestine.

For this study, researchers compared the risk of clotting in patients with IBD, rheumatoid arthritis and celiac disease with a set of control subjects.

In all, the study included 618 patients with IBD, 243 with rheumatoid arthritis and 207 with celiac disease, along with 707 healthy controls. All were asked to fill out questionnaires regarding previous blood clots. Positive answers were then confirmed radiologically.

Thirty-eight IBD patients (6.2 percent of the total) turned out to have suffered clots, a rate 3.6 times that of the control group (only 10 cases, or 1.6 percent). The risk for clotting seemed to increase with age in this group of participants and was more evident when the patient had active disease.

Participants with rheumatoid arthritis or celiac disease had about the same risk of clotting as the controls did.

The researchers did not know why the risk of blood clots is higher in IBD than other disorders, nor could they definitively state the relationship is a cause-and-effect one.

But the study's senior author, Gottfried Novacek of the University of Vienna in Austria, does have some hypotheses.

"From the clinical point of view, active disease and complications of Crohn's disease such as stenosis, fistulas and abscess seem to be the most important factor, since we found such situations in two-thirds of patients at the time of thrombosis," he says. "I believe that inflammation and inflammatory mediators kindle blood clotting in IBD. Additionally, patients with IBD may need surgical treatment during their life, and some of the thromboembolic events happened postoperatively."

Clain notes, "The only thing [the study] really adds is to say, if the mechanism was due to some general systemic inflammatory response, then it should have shown up in other general systemic inflammatory conditions like rheumatoid arthritis, and it didn't."

"It suggests something more special is happening in inflammatory bowel disease," Clain adds.

Novacek feels the results do indicate a direction for future research. "The abnormalities found may suggest increased blood clotting but were not able to establish a causal relationship," he says. "We need studies which include enough patients with IBD and thrombosis. . . The researchers have to look for clinical conditions at the time of the thromboembolic events and parameters and factors, which are of importance for the development of thrombosis."

More information

The National Digestive Diseases Information Clearinghouse has more on inflammatory bowel disease and celiac disease. The Arthritis Foundation has more on rheumatoid arthritis.

(SOURCES: David Clain, M.D., associate chief, division of gastroenterology and liver diseases, Beth Israel Medical Center, and professor, clinical medicine, Albert Einstein College of Medicine, both in New York City; James Smith, M.D., section head, gasteroenterology and hepatology, Ochsner Clinic Foundation, New Orleans; Gottfried Novacek, University of Vienna, Austria; April 2004 Gut)

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