Even if a patient had a previous clear colonoscopy or all polyps seen on that exam were removed, a new positive fecal occult blood test (FOBT) calls for a repeat colonoscopy.
After 21,600 clear colonoscopies done at the Veterans Administration Medical Center in Phoenix, 57 patients needed a second colonoscopy after they had a positive FOBT for blood in their stool. Of those one-third (19) had a newly discovered adenomatous polyp and 3 had colon or rectal cancer. One in four of the new adenomas were advanced.
Nine of the patients with a new polyp or cancer had a history of polyps or cancer. Less than optimal bowel preparation for the initial colonoscopy was also associated with finding a new lesion.
Other reasons for blood in the stool included hemorrhoids in two-thirds of patients and diverticulosis in almost half.
Dr. Brindusa Truta, of the Phoenix VA Medical Center emphasized,
A positive fecal occult blood test after a ‘cleared’ colonoscopy should trigger a repeat colonoscopy, especially if a suboptimal bowel preparation was encountered at the initial exam.
SOURCE: Truta et al., The yield of repeat colonoscopy for a positive fecal occult blood test (FOBT) after a prior “cleared” colonoscopy, American College of Gastroenterology Annual Scientific Meeting, October 7, 2008.