Positive predictive value of fecal occult blood testing in persons taking warfarin

In clinical practice, some physicians discontinue warfarin prior to fecal occult blood testing (FOBT). Although anticoagulant use is associated with an increased risk of overt gastrointestinal bleeding, the impact of warfarin on the positive predictive value of FOBT is unknown.

During a 5-yr period, we prospectively studied all patients taking warfarin who were referred for the evaluation of a positive FOBT. For each patient taking warfarin, we enrolled one age- and gender-matched control subject with a positive FOBT who was not taking anticoagulants. A detailed clinical history was obtained, and all subjects underwent colonoscopy and esophagogastroduodenoscopy.

Lesions consistent with occult bleeding were identified in 59.0% of the 210 patients in the warfarin group and 53.8% of the 210 control subjects (p= 0.27). Although more lesions were identified by colonoscopy in the warfarin group than in control subjects (36.2%vs 25.7%, p= 0.02), there was no difference in the frequency of lesions identified by esophagogastroduodenoscopy (35.2%vs 39.5%, p= 0.43). Overall, adenomas > or =1 cm in diameter (16.2%) and colorectal carcinoma (9.5%) were the most common lesions identified by colonoscopy, while erosive gastritis (15.5%) and erosive duodenitis (11.0%) were the most frequent lesions found by esophagogastroduodenoscopy. Among individuals with colorectal cancer, 83.3% of patients in the warfarin group had early cancers (Dukes' stage A or B) compared with 50.0% of control subjects (p= 0.046).

Warfarin use did not decrease the positive predictive value of FOBT. These findings suggest that warfarin should not be discontinued prior to FOBT.