Fecal Occult Blood Test in Patients on Low-Dose Aspirin, Warfarin, Clopidogrel, or Non-steroidal Anti-inflammatory Drugs

To determine the effect of anticoagulants and antiplatelet medications on the positive-predictive-value of fecal occult blood test (FOBT).

All patients who underwent a colonoscopy at our institution from 1995 to 2006 for a positive FOBT were identified. Medical records were searched, and patients were stratified into five groups selected a priori: low-dose aspirin, NSAIDs, warfarin, clopidogrel, or controls. The positive-predictive-value of FOBT for advanced colonic neoplasia was computed for each group.

During the study period, 1,126 patients underwent colonoscopy for a positive FOBT and met entry criteria. The average age of study participants was 69 years and most were men. The positive-predictive-value of FOBT for advanced colon neoplasia was significantly higher in the control group (30.5%) when compared to those on low-dose aspirin (20.5%; p = 0.003), NSAIDs (19.7%; p = 0.003), clopidogrel (7.3%; p = 0.002), or warfarin (20%; p = 0.05). The positive-predictive-value of FOBT was significantly lower for those on clopidogrel than those on low-dose aspirin (p = 0.04) and NSAIDs (p = 0.05), but not warfarin (p = 0.08). The positive-predictive-value for FOBT was similar for those on aspirin, NSAIDs, and warfarin. There was a linear trend between the number of number of positive FOBT cards and prevalence of advanced colon neoplasia (p = 0.01).

Anticoagulants and antiplatelet medications lower the positive-predictive-value of FOBT for advance colonic neoplasia and should be stopped if clinically feasible prior to stool collection.