Systematic review with meta-analysis: faecal occult blood tests show lower colorectal cancer detection rates in the proximal colon in colonoscopy-verified diagnostic studies

BackgroundThe performance of faecal occult blood tests (FOBTs) to screen proximally located colorectal cancer (CRC) has produced inconsistent results. AimTo assess in a meta-analysis, the diagnostic accuracy of FOBTs for relative detection of CRC according to anatomical location of CRC. MethodsDiagnostic studies including both symptomatic and asymptomatic cohorts assessing performance of FOBTs for CRC were searched from MEDINE and EMBASE. Primary outcome was accuracy of FOBTs according to the anatomical location of CRC. Bivariate random-effects model was used. Subgroup analyses were performed to evaluate test performance of guaiac-based FOBT (gFOBT) and immunochemical-based FOBT (iFOBT). ResultsThirteen studies, with 17 cohorts, reporting performance of FOBT were included; a total of 26342 patients (mean age 58.9years; 58.1% male) underwent both colonoscopy and FOBT. Pooled sensitivity, specificity, positive likelihood ratio and negative likelihood ratio of FOBTs for CRC detection in the proximal colon were 71.2% (95% CI 61.3-79.4%), 93.6% (95% CI 90.7-95.7%), 11.1 (95% CI 7.8-15.8) and 0.3 (95% CI 0.2-0.4) respectively. Corresponding findings for CRC detection in distal colon were 80.1% (95% CI 70.9-87.0%), 93.6% (95% CI 90.7-95.7%), 12.6 (95% CI 8.8-18.1) and 0.2 (95% CI 0.1-0.3). The area-under-curve for FOBT detection for proximal and distal CRC were 90% vs. 94% (P=0.0143). Both gFOBT and iFOBT showed significantly lower sensitivity but comparable specificity for the detection of proximally located CRC compared with distal CRC. ConclusionFaecal occult blood tests, both guaiac- and immunochemical-based, show better diagnostic performance for the relative detection of colorectal cancer in the distal colon than in the proximal bowel.