Is fecal occult blood testing more sensitive for left-sided than for right-sided advanced colorectal neoplasms? Literature review and evidence from a large screening study

Background: Fecal occult blood tests (FOBTs) are widely used for colorectal cancer screening. The aim of this study was to assess whether there is a difference in sensitivity of FOBTs for advanced colorectal neoplasms in the left versus the right colon. Methods: We systematically searched the literature for screening studies conducted in average-risk adults that performed a FOBT (immunochemical and/or guaiac-based) and colonoscopy among all participants and reported site-specific sensitivities of the FOBT for advanced colorectal neoplasms. We further analyzed fecal occult blood levels measured by an immunochemical FOBT (RIDASCREEN®) in 2204 subjects at average risk for colorectal neoplasia who underwent screening colonoscopy. We constructed receiver-operating characteristics (ROC) curves stratified by left-sided and right-sided advanced neoplasms, taking into account comparability between subgroups with respect to findings at colonoscopy. Results: Seven articles were included in the review, showing consistently higher sensitivities for advanced neoplasms in the left than in the right colon for different types of FOBTs. Our data analyses showed a significantly larger area under the ROC curve for left-sided than for right-sided advanced neoplasms (p<0.05), even when only subjects with one large adenoma (in the left or in the right colon) were included as cases. Conclusion: Both the literature review and our primary data analysis strongly support the hypothesis that FOBTs are more sensitive for detecting left-sided advanced colorectal neoplasms. This finding implies limited potential for FOBTs in terms of protecting from right-sided CRC and should be taken into account when estimating the effectiveness and cost-effectiveness of FOBT-based screening strategies.