Fecal Occult Blood Tests: False-Positive Results

Do aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) cause false-positive results in fecal occult blood tests?

Apparently not, according to a study at the Roudebush Veterans Affairs Medical Center in Indianapolis, Indiana. Of 193 patients referred for colonoscopy after a positive fecal occult blood result, 135 used aspirin or NSAIDs regularly (at least one daily dose for at least three days a week). The researchers found no difference between regular aspirin or NSAID users and patients who did not use the drugs in terms of the prevalence of colonoscopic findings that would potentially explain a positive result.

Twenty-nine patients (21%) had findings that could explain the positive result, compared with 11 (19%) of 58 patients who did not use the drugs.

Among regular aspirin users, there was no relationship between the dose of aspirin and the likelihood of explanatory colonic findings. The lack of association held, even after adjustment for factors such as age, body mass index, a family history of colorectal cancer, and the use of proton-pump inhibitors or histamine-2 receptor antagonists.