More Support for Fecal Immunochemical Testing

Many studies have indicated that immunochemical testing is superior to guaiac-based testing for detecting fecal occult blood. Adding to this evidence base is a French study, in which 10,673 average-risk adults completed both standard guaiac-based testing (nonrehydrated Hemoccult II) and quantitative immunochemical testing (Immudia/RPHA). Of the 886 study participants who had positive results on one or both tests, 644 underwent colonoscopy. Of these, 294 had adenomas or cancer.

The immunochemical test outperformed the guaiac-based test at every evaluated hemoglobin threshold. At the usual threshold of 20 ng/mL, the immunochemical test identified 50% more cancers and 256% more high-risk adenomas than did the guaiac-based test. However, the increased sensitivity resulted in lower specificity, such that 47 false-positive results would be required to detect 1 extra case of invasive colorectal cancer, and 2.2 false-positive results would be required to detect 1 extra advanced adenoma. With a threshold of 50 ng/mL, the immunochemical test detected 2.3 times as many advanced neoplasias as the guaiac-based test did, with no loss of specificity. At a threshold of 75 ng/mL, the overall rate of positive results on the immunochemical test was similar to that of the guaiac-based test (2.4%), with a 90% gain in sensitivity and an actual improvement in specificity (a 33% reduction in false positives).