Fecal occult blood testing: a false sense of security?

BACKGROUND

Recent screening studies with fecal occult blood testing (FOBT) report that one of three patients with colorectal cancer (CRC) can be cured of the disease; minimal attention has been given to the two of three patients who despite repeated screening go on to die of silent CRC. We report the known "miss rate" (known false negatives) of our 14-year ongoing program of FOBT that was organized in 1979 to detect early CRC.

METHODS

From October 1979 through December 1993, 36,034 FOBT kits were distributed to patients who were without gastrointestinal complaints at Hines Veterans Affairs Hospital. The test was considered positive if at least one result of the six tests was positive and negative if the test result was equivocal. Patients with negative FOBT received a new test kit each year by mail. A positive test was followed by full colonoscopy or an air contrast barium enema if a full colonoscopy was not possible.

RESULTS

The overall return rate was 47.8%. CRC was detected in 115 patients: 94 had a favorable and 21 had an unfavorable Duke's C or D or lymphoma prognosis. Of 21 patients 13 (62%) had initially tested FOBT negative (missed lesion). Of the 21 cases of advanced CRC 15 (71.43%) were in the descending, sigmoid, or rectosigmoid colon or rectum.

CONCLUSIONS

(1) The majority (82%) of all CRC detected by FOBT screening are diagnosed at a favorable stage. (2) The majority of known advanced CRC (62%) escape early detection with FOBT. (3) Five (62.5%) of eight of the advanced CRC cases discovered on initial FOBT and 10 (76.9%) of 13 of advanced CRC cases missed on initial FOBT but detected in subsequent years were in the left colon and most likely in the range of the flexible sigmoidoscope. (4) FOBT as a sole screening test may provide a false sense of security, especially in patients with advanced left-side CRC.