Fecal occult blood testing for colorectal cancer screening: use the finger

Fecal occult blood testing (FOBT) has been widely underused as a means of colorectal cancer screening. Less than 35% of Americans have had the recommended FOBT in the last 5 yr. Guidelines suggest FOBT of three spontaneously passed stools (SPS) on a prescribed diet. Testing stool obtained by digital rectal exam (DRE) is discouraged because its yield in colorectal cancer screening is unknown. The aim of this study is to compare the positive predictive value of FOBT for the detection of colorectal neoplasia done by SPS versus DRE in asymptomatic outpatients.

Medical records and endoscopic reports of all patients who underwent colonoscopy between 1984-1999 for a positive FOBT were reviewed. Only asymptomatic outpatients whose indication was colorectal cancer screening were included. The method of FOBT was confirmed as either SPS or DRE. Chi2 was used to compare the yield of detecting colorectal neoplasia between SPS and DRE.

A total of 165 patients with a mean age of 61 yr (range 33-85) were included (84 patients were women). Neoplasia was detected in 29 of 80 (36%) with SPS and 28 of 85 (33%) with DRE (p = 0.18).

The positive predictive value of FOBT on DRE for detecting neoplasia is similar to that of SPS in asymptomatic outpatients undergoing colorectal cancer screening. Positive FOBT on DRE warrants colonoscopic evaluation. Hemoccult testing by DRE may be performed in the office to increase patient compliance with colorectal cancer screening. A negative FOBT on DRE should be followed up with FOBT of SPS.