Endoscopy and the Risk of Venous Thromboembolism: A Case-Control Study

Background and Study Aims To assess whether there was an association between endoscopy and the risk of venous thromboembolism (VTE). Patients and Methods Retrospective case - control study of patients diagnosed with VTE over a 3-year period. Each was age- and sex-matched to one of three controls who attended an outpatient appointment on the same date as that of the diagnosis of VTE in the patients. Patients who had undergone endoscopy within 90 days of VTE were included. On a second analysis, patients who were hospitalized and those with inflammatory bowel disease or malignancy were excluded. The difference in occurrence of endoscopy between cases and controls was examined using the McNemar test. The risk of VTE occurring following endoscopy was quantified by means of odds ratios. Results Forty-five of 436 patients (10.3 %) had undergone an endoscopy in the VTE group compared with 14 /436 controls (3.2 %; P < 0.001). The odds ratio for developing a VTE after an endoscopic procedure was 3.58 (95 % CI 1.86 - 7.46) for patients relative to controls. When the 10 hospitalized patients and respective controls were excluded, the odds of VTE remained nearly 3 times as large for patients undergoing endoscopy as for controls (2.92 [95 % CI 1.51, 5.62]; P = 0.001). When patients with inflammatory bowel disease or malignancy were also excluded, no difference was found between patients undergoing endoscopy and controls (1.92 [0.95, 3.85]; P = 0.07). Ten percent of patients with VTE underwent endoscopy in the 3 months before the diagnosis compared with 3 % of controls (P < 0.001). No significant difference was found between the type of endoscopy performed and VTE risk. Conclusions When those with known risk factors for VTE were excluded, no significant increased risk of VTE was found.