Fecal Occult Blood Test Performance Indicators in Warfarin-Treated Patients

BACKGROUND: Antithrombotic drugs such as warfarin cause a general increase in bleeding tendency and therefore could influence fecal occult blood test results. METHODS: A population-based retrospective cohort study was conducted to investigate the performance of the fecal occult blood test for colorectal cancer screening in patients taking warfarin. The study population included 1356 tests performed in warfarin-treated patients and 64,088 tests in those not taking antithrombotics. Data on lower gastrointestinal evaluation were collected on 425 cases with a positive fecal occult blood test: all positives on warfarin and positive cases of a subsample of those tests in the group without antithrombotic treatment. RESULTS: The positivity rate of the fecal occult blood test in the warfarin group was found to be doubled (7.7% (95%CI, 6.3%-9.2%)) compared with those not taking antithrombotics (3.6% (95%CI, 3.4%-3.7%)) (P <.0001). No significant difference in the positive predictive value for carcinoma and significant adenomas was found comparing the warfarin group to the no-antithrombotic group. The detection rates of both clinically significant adenomas and findings not indicative of significant neoplasia were increased in the warfarin group (8.9/1000 and 32.5/1000 respectively) compared with the no-antithrombotic group (4.0/1000 and 11.3/1000) (P = .02 and P <.0001 respectively), whereas that of carcinoma was not found to be different (3.7/1000 in the warfarin group vs 3.3/1000, P = .85). CONCLUSIONS: Fecal occult blood test screening in warfarin users results in a higher, yet reasonable, positivity load and in a higher detection of premalignant lesions than in the general population. We consider fecal occult blood test screening appropriate for the warfarin-taking population.