Objectives: The fecal occult blood test (FOBT) is widely used for colorectal cancer screening. However, the impact of warfarin use on FOBT sensitivity and specificity remains unclear. This study compares the relative risk of neoplasia in FOBT-positive patients stratified by warfarin use.
Methods: The Clinical Outcomes Research Initiative database was used to identify patients with positive FOBT as the only indication for colonoscopy during 2005-2006. Patients were categorized on the basis of documented warfarin status within a 30-day period before FOBT. We compared the demographics and prevalence of significant colon findings (defined as polyp >9 mm or suspected malignant tumor) among the two groups. After adjusting for confounding variables, logistic regression was used to estimate the odds ratio of significant findings in warfarin-positive vs. warfarin-negative patients.
Results: Of 10,266 patients with positive FOBT, 372 used warfarin, 9,265 did not use warfarin, and 629 were excluded because of missing warfarin status. Warfarin-positive patients were more likely male (65 vs. 50%; P<0.0001), Caucasian (88 vs. 80%; P<0.0001), and veterans (53 vs. 33%; P<0.0001). The prevalence of a significant finding was greater in the warfarin group, 16 vs. 11.4% (P<0.01). After adjusting for age and sex, the relative risk of significant colon findings among warfarin-positive patients was not significantly different from warfarin-negative patients (odds ratio 1.1, 95% confidence interval: 0.81-1.44).
Conclusions: No increased risk for significant colonic findings among FOBT-positive patients according to warfarin use was identified. These findings suggest that continuing warfarin before FOBT will not affect the positive predictive value of this screening test.