Effect of Verification Bias on the Sensitivity of Fecal Occult Blood Testing: a Meta-Analysis

Abstract

OBJECTIVES: There is controversy regarding the sensitivity of fecal occult blood tests (FOBT) for detecting colorectal cancer. Many of the published studies failed to correct for verification bias which may have increased the sensitivity. METHODS: A meta-analysis of published studies evaluating the sensitivity and specificity of chemical-based FOBT for colorectal cancer was performed. Studies were included if both cancer and control subjects underwent confirmatory testing. We also included studies that attempted to correct for verification bias by either performing colonoscopy on all subjects regardless of the FOBT result or by using longitudinal follow-up. We then compared the sensitivity, specificity, and other diagnostic characteristics of the studies that attempted to correct for verification (n=10) vs. those that did not correct for this bias (n=19). RESULTS: The pooled sensitivity of guaiac-based FOBT for colorectal cancer of studies without verification bias was significantly lower than those studies with this bias There was no significant difference in the area under the summary receiver operating characteristic curves. More sensitive chemical-based FOBT methods (e.g., Hemoccult® SENSA®) had a higher sensitivity but a lower specificity than standard guaiac methods. CONCLUSIONS: The sensitivity of guaiac-based FOBT for colorectal cancer has been overestimated as a result of verification bias. This test may not be sensitive enough to serve as an effective screening option for colorectal cancer.KEY WORDS: fecal occult blood; guaiac; colorectal cancer; summary receiver operating characteristic curve; meta-analysis.

Diagnostic value of fecal tumor M2‐pyruvate kinase for CRC screening: A systematic review and meta‐analysis

“…Furthermore, it was reported that gFOBT had a low positive predictive value and over 80% of its positive results were false 42. A meta‐analysis that evaluated the effect of verification bias on the sensitivity and specificity of gFOBT showed the existence of verification bias, which could largely affect the estimates of gFOBT, the pooled sensitivity and specificity of the studies without verification bias turns out to be 0.36 (95% CI = 0.25–0.47) and 0.96 (95% CI = 0.94–0.97) 43. In our head‐to‐head comparison of fecal PKM2 and gFOBT for diagnosis of CRC, all the patients accepted the colonoscopy exam as the reference test; thus, the results could be thought of as nonverification bias.…”

Verification bias

“…A meta-analysis comparing the diagnostic accuracy of FOBT for colorectal cancer found that the pooled sensitivity of FOBT without verification bias was significantly lower than those studies with this bias (0.36 vs 0.70). The pooled specificity of the studies without verification bias was also higher (0.96 vs 0.88) 4. The authors concluded that ‘the sensitivity of guaiac-based FOBT for colorectal cancer has been overestimated as a result of verification bias.…”

Diagnostic inconsistency of faecal immunochemical tests for haemoglobin in population screening of colorectal cancer

“…The guaiac-based FOBT (gFOBT) is the typical test of the early FOBT products. However, the later developed faecal immunochemical test (FIT) for haemoglobin has been shown to be better than the original gFOBT [1]. It has better sensitivity and specificity for predicting colorectal neoplasms in an asymptomatic population [2].…”