Diagnostic accuracy of immunochemical versus guaiac faecal occult blood tests for colorectal cancer screening

Immunochemical tests show important advantages over chemical-based faecal occult blood tests (FOBT) for colorectal cancer (CRC) screening, but comparison studies are limited. This study was performed to compare the accuracy of a sensitive immunochemical test with the guaiac test for detecting significant neoplasia (advanced adenomas and CRC) in an average-risk population. A random sample of 2288 asymptomatic subjects 50-79 years of age was prospectively included. Participants received three cards of the guaiac test, one sample of a latex-agglutination test (haemoglobin cut-off 50 ng/ml), and an invitation to undergo colonoscopy. Test sensitivity, specificity, and positive and negative predictive values (PPV and NPV) were calculated in 1756 compliers. Immunochemical and guaiac tests were positive in 143 (8.1%) and 62 (3.5%) subjects, respectively. Complete colonoscopy, performed in 402 participants (158 FOBT+ and 244 FOBT-), detected 14 (0.8%) patients with CRC and 49 (2.8%) with advanced adenomas. The immunochemical and guaiac tests for significant colorectal neoplasia showed sensitivities of 61% versus 23.8%, specificities of 95.1% versus 97.7%, PPVs of 43.4% versus 39.0%, and NPVs of 97.5% versus 95.4%, respectively. Proximal significant neoplasms were more frequently detected with the immunochemical test (85% vs. 15%) The relative risk for detecting significant neoplasia was superior in patients with a positive immunochemical test (RR 16.93; CI 7.94-36.10) than with a positive guaiac test (RR 3.34; CI 2.17-5.15). A sensitive immunochemical test is markedly superior to the guaiac test for detecting significant colorectal neoplasia, and should be considered the first-choice FOBT for CRC screening in the average-risk population.