Patients with inflammatory bowel disease (IBD) are at increased risk of venous thromboembolism (VTE), especially during periods of disease flare-up according to a large epidemiological study reported in the Lancet.

VTE is associated with significant morbidity and mortality, and there is evidence that patients with IBD may be at increased risk during periods of active disease. The absolute risk for those not admitted to hospital is uncertain, and the authors of this study aimed to quantify it using data from the UK GPRD. Participants were patients included in the GPRD who had prospectively recorded IBD between November 1987 and July 2001; each patient was matched with up to five controls. The study period was from IBD diagnosis to end of follow-up, and a disease flare was defined as prescription of a corticosteroid after a corticosteroid-free period of at least four months. VTE was identified from the patient records, and the risk for each patient was estimated with time according to whether they were in remission, in a disease flare, or in a chronic state.

There were 13,756 eligible patients with IBD and 71,672 matched controls for analysis; 139 patients and 165 controls developed VTE during follow-up. Patients were at significantly increased risk of VTE overall (hazard ratio [HR] 3.4; 95% CI, 2.7 to 4.3; p<0.0001; absolute risk 2.6 per 1000 per person-years). Their risk during disease flare-up was significantly greater still (HR, 8.4; 95% CI, 5.5 to 12.8; p<0.0001; 9.0 per 1000 person-years). During disease flares, patients’ relative risk was significantly greater if they were not hospitalised than if they were (relative risk 15.8 vs. 3.2).

The authors conclude that patients with IBD are at significantly increased risk of VTE compared to controls, and that this risk is increased more than two-fold during periods of disease flare. These patients’ risk is greater than that during pregnancy and post-partum, and similar to that of people with cancer. As a result, they conclude that trials of primary prophylaxis for VTE in this group are warranted.

An accompanying Comment article discusses the study. The authors comment that primary prevention trials might be difficult as the absolute risk is low, however a pragmatic approach including patient education and physical methods may be justified. Additional studies are needed to establish prevalence.