Venous thromboembolism (VTE) is 16 times more likely to strike a nonhospitalized person with inflammatory bowel disease (IBD) than the nonhospitalized general public, a new study reveals.

Individuals who have ulcerative colitis, Crohn’s disease, or other forms of IBD are known to be particularly at risk for blood clots during hospital stays; current research suggests that most people with IBD have active disease at the time they develop VTE. However, the risks among people with IBD who are not hospitalized had been unknown until researchers undertook a study funded by the National Association for Colitis and Crohn’s Disease.

The analysis included 13,756 people with IBD and 71,672 matched controls, with data spanning 14 years. A total of 139 IBD patients and 165 controls developed VTE. Overall, the IBD patients had a 3.4-times increased risk for blood clots than did the controls, but the risk became considerably more prominent during a symptom flare, reaching eight times increased risk. Although the absolute risk was greater for IBD patients in the hospital, this relative risk at the time of a flare was higher during periods of nonhospitalization, when patients were found to be 16 times more likely to suffer a blood clot than were their nonhospitalized controls.

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“Despite the low absolute risks during nonhospitalized periods, these results suggest that active IBD in ambulatory patients may be a far greater risk factor for VTE than previously recognized,” cautioned the researchers (Lancet. 2010;375:657-663).

Clinicians should work to reduce the risk of VTE in nonhospitalized people who are suffering from IBD flares.