Quantitative colonoscopic evaluation of relative efficiencies of an immunochemical faecal occult blood test and a sensitive guaiac test for detecting significant colorectal neoplasms

Background: The guaiac faecal occult blood test (G-FOBT), HemoccultSENSA, is sensitive for significant neoplasms [colorectal cancer (CRC), advanced adenomatous polyps (AAP)], but faulted by non-specificity for human haemoglobin (Hb). Quantified, Hb- specific, immunochemical faecal occult blood tests (I-FOBT) are now used. Aims: To (i) compare I-FOBT and G-FOBT efficacy in identifying significant neoplasms and colonoscopy needs for positive tests and (ii) examine number of I-FOBTs needed and test threshold to use for equivalent or better sensitivity than G-FOBT and fewest colonoscopies for positive tests. Methods: Three daily G-FOBTs and I-FOBTs were collected and analysed in 330 patients scheduled for colonoscopy. Results: Colonoscopy found significant neoplasms in 32 patients, 6 CRC, 26 AAP. G-FOBT, sensitivity and specificity were 53.1% (17 neoplasms) and 59.4%, resulting in 8.1 colonoscopies/neoplasm. One I-FOBT having ≥50 ngHb/mL of buffer provided equivalent sensitivity but 94.0% specificity, resulting in 2.1 colonoscopies/neoplasm. By analysing the higher of two I-FOBTs at 50 ngHb/mL threshold, sensitivity increased to 68.8% (22 neoplasms, P = 0.063), specificity fell to 91.9% (P < 0.001), but still required 2.1 colonoscopies/neoplasm. Conclusions: In this population, quantified I-FOBT had significantly better specificity than G-FOBT for significant neoplasms, reducing the number of colonoscopies needed/neoplasm detected. Results depend on the number of I-FOBTs performed and the chosen development threshold.