Dietary restrictions and fecal occult blood testing.

"Unprepped" sigmoidoscopy and fecal occult blood testing were performed simultaneously in 1,000 patients with no dietary restrictions. A total of 102 patients had a positive fecal occult blood test. Of these, 86 had visible blood in the rectum as demonstrated by sigmoidoscopy. Only two of the remaining 16 patients probably had a dietary-induced false-positive result on the occult blood test. Dietary restrictions for guaiac occult blood testing are unnecessary in more than 99 percent of patients.