Ulcerative Colitis Is Associated With an Increased Risk of Venous Thromboembolism in the Postoperative Period

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To the Editor:
We commend Dr Wilson and colleagues1 for their important contribution to the evidence base on the role of extended venous thromboembolism (VTE) prophylaxis for patients with ulcerative colitis (UC).
Extended VTE prophylaxis after major abdominal cancer surgery is now standard care.2 This is supported by randomized controlled trial evidence that extended VTE prophylaxis reduces the likelihood of VTE by 57.3%.3 A recent trial has suggested that extended prophylaxis may even reduce the risk of VTE after laparoscopic colorectal cancer surgery to zero.4 Importantly, extended prophylaxis was found to be safe in this trial, with no increase in hemorrhagic complications.
There are no equivalent guidelines on extended VTE prophylaxis after colectomy for UC. The methodology of Wilson and colleagues is likely to produce the best possible evidence to inform any such guidelines, as a randomized controlled trial of extended prophylaxis in UC is likely to be impractical. Although amongst other indications for colectomy, UC was found to be associated with the greatest risk of postoperative VTE, the rate was low at 2.74%. As such, more than a thousand patients would be needed to power a trial attempting to detect a 60% reduction in the VTE rate that has been identified after extended prophylaxis in cancer patients.3
The finding by Wilson and colleagues that patients with inflammatory bowel disease (IBD) have a greater risk of postoperative VTE than cancer patients has been replicated by another study analyzing the same data set with different methodology.5 The matched cohort analysis methodology of Wilson and colleagues is superior, as propensity score matching has reduced the bias resulting from UC patients being younger and having fewer established VTE risk factors than patients operated on for other indications. Unfortunately, Wilson and colleagues have been unable to risk adjust for 3 crucial variables: history of VTE events, the extent of the resection performed, and whether patients actually received any VTE prophylaxis, either in hospital or extended into the postdischarge recovery phase. It should also be noted that the impact of extended prophylaxis is likely to be lower outside of clinical trials, given that compliance with prescribing of extended prophylaxis for patients with colorectal cancer may be as low as 1.5% in some centers.6
The primary endpoint of Wilson and colleagues was the VTE rate at 30 days postoperatively. This may represent inadequate follow-up, as a study of medical patients after IBD-related hospitalization found VTE events to sequentially increase with each additional month of follow-up, with the rate at 180 days almost triple that at 30 days.7
Wilson and colleagues found that at 30-day follow-up, 41.5% of VTE events in UC patients occurred postdischarge. On the basis of data from Wilson and colleagues, the number needed to treat (NNT) to prevent 1 VTE event would be approximately 200, assuming that absolute compliance with prescribing and administration of extended VTE in UC patients results in a similar reduction in VTE rates to that identified in cancer patients.3
A high NNT could be justified if extended prophylaxis were to reduce the risk of significant complications. The current study included all patients with symptomatic deep vein thrombosis and pulmonary emboli, but it provides no data concerning the severity of these complications. It has previously been found that up to a quarter of IBD patients suffering from VTE require intensive care and 1 in 10 patients die.8
Extended subcutaneous administration of low-molecular-weight heparin is broadly accepted by patients.9 In postoperative UC patients, it is likely to be effective in reducing morbidity associated with VTE events, even if a low risk of VTE remains.

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