Diagnosis reliability of combined flexible sigmoidoscopy and fecal-immunochemical test in colorectal neoplasia screening

Background: Employing colonoscopy, the gold standard in colorectal cancer (CRC) diagnosis testing, for CRC screening presents a significant risk of complications. Alternative methods with a lower invasive-level and fewer risks are proposed in combination, though each with lower diagnosis performance when applied separately. The main objective of this cross-sectional pilot study was to evaluate the feasibility of a CRC screening program using combined flexible sigmoidoscopy and fecal-immunochemical test (FIT). Methods: The patient population consisted of 2,201 consecutive-case symptomatic patients attending the gastroenterology outpatient clinic with mild complaints between 2012 and 2014. They were referred for FIT. A sample of 252 individuals underwent a subsequent colonoscopy, blind to FIT results, and theoretical sigmoidoscopy was simulated. On a subsample of 57 patients, real sigmoidoscopy was additionally performed. Prior probabilities in terms of patients' compliance and CRC prevalence were estimated, together with predictive ability of FIT and sigmoidoscopy in screening population. We assessed the merit of a screening strategy employing two-stage serial multiple testing: a) first stage by combining two parallel tests, that is, flexible sigmoidoscopy and FIT and b) colonoscopy as the second diagnosis test. The scheme was validated using the actual predictive values derived from the study population. Results: Colonoscopy found 75 (29.76%) individuals with advanced neoplasia. FIT was positive in 30.3% of advanced neoplasia cases, while between 23.73% and 28.28% met the theoretical sigmoidoscopy simulation criteria, with good concordance between real and theoretical sigmoidoscopy. The colonoscopy referral compliance rate was 52% among FIT-positives. Sensitivity and specificity of the first-stage test combination were better than sigmoidoscopy alone (McNemar test: P<0.001). Negative predictive values for low prevalence levels were between 81.5% and 90.12%. Conclusion: Combining less resource challenging and less invasive testing procedures is worthwhile in colorectal neoplasia detection, improving sensitivity and specificity of either test alone, and leading to better posterior probabilities in usual screening scenarios.