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NEW YORK (Reuters Health) - People with active forms of a group of conditions known as inflammatory bowel disease, or IBD, seem to be at far greater risk of developing potentially life-threatening blood clots than previously recognized, a British study released Monday indicates.The study, appearing in the Lancet, found that non-hospitalized patients dealing with an IBD flare-up are 16 times more likely to suffer a blood clot in a vein than the general (non-hospitalized) population. That translates into about a one in 100 risk per person with IBD per year. Such clots, which often develop in the legs, sometimes travel to the lungs and can become life-threatening.IBD refers to a group of conditions, including Crohn's disease and ulcerative colitis, marked by chronic inflammation in the intestines, leading to symptoms like belly pain and diarrhea. And while medication can keep the disease at bay, flare-ups are common. Researchers suspect that the inflammation seen in IBD, plus the increased likelihood of infection among patients with the condition, is responsible for the higher blood clot risk."While the absolute risk is low and similar to that in women who are pregnant" - who are known to have a slightly higher risk than the average population -- "the increased risk we have demonstrated for patients with active disease outside hospital means that their doctors should regard them as a high-risk group during these times," study co-author Dr. Matthew J Grainge, of University of Nottingham, told Reuters Health by email.It is generally accepted that when in the hospital, the risk of blood clots in IBD patients is high enough to warrant preventive measures, such as blood thinners, which carry their own risks, Grainge explained. However, "the benefit of using such measures when not in hospital has not been studied so we do not know whether they work."In fact, until now, information on the risk of blood clots forming in people with IBD who are not in the hospital was lacking.Grainge's team examined the medical records of more than 13,700 adults with IBD and more than 71,600 people from the general population without the condition. Of these, 139 people with IBD and 165 without developed a blood clot.Overall, IBD was associated with about a three-fold increased risk of blood clots, a figure similar to that found in earlier studies. That meant about three clots per 1,000 people per year, the researchers point out. But at the time of a flare-up in IBD activity, the risk of a blood clot was roughly eight-fold higher, which translated to nine per 1,000 people per year.Whether people were in the hospital during a flare-up also played a role in blood clot risk. Among those in the hospital during a flare-up, there were about 38 clots per 1,000 people per year, compared to many fewer, about six clots per 1,000 people per year, for those not hospitalized during a flare-up.In an email to Reuters Health, Dr. Geoffrey C. Nguyen, of Mount Sinai Hospital IBD Centre at the University of Toronto, Canada, who co-authored a Lancet commentary on the study, said "it is important for patients to be educated by physicians that their IBD puts them at increased risk of blood clots, particularly when they are having flares." Should IBD patients take blood thinners outside the hospital during flares? Not just yet, said Nguyen. "Having patients giving themselves injections at least once a day can be hard for the patient and we don't know how long patients should be taking these blood thinners," he told Reuters Health. "Until we can show that they are of clear benefit in the IBD population, I think is premature to make general recommendations for their use during an IBD flare."In the meantime, Nguyen and his co-author say a "pragmatic initial approach" to curbing the risk of blood clots in IBD patients outside the hospital would be non-drug prevention tactics, including increasing IBD patients' awareness of the risk and of the signs of a possible blood clot such as pain in the calf or leg, as well as possibly the use of support stockings, which help prevent fluid from pooling in the legs.