Colorectal Cancer Screening by Fecal Immunochemical Tests (FIT): Considerations on Sampling and Markers (Hb and Hb/Hp Complex) of Fecal Occult Blood (FOB).

Background/aim: Formal demonstration of the efficacy of colorectal cancer (CRC) screening by fecal immunochemical tests (FITs) in reducing CRC incidence and mortality is still missing. The aim of this study was to analyze the impact of sampling and FIT marker in the recently implemented CRC screening program in Finland.

Patients And Methods: Because only the index test [FIT hemoglobin (Hb)]-positive subjects are verified by the reference test (colonoscopy), the new screening program is subject to verification bias that precludes estimating the diagnostic accuracy (DA) indicators. A previously published study (5) with 100% biopsy verification of colonoscopy referral subjects (called validation cohort, n=300) was used to derive these missing DA estimates. Two points of concern were addressed: i) only one-day sample tested, and ii) only the Hb component (but not Hb/Hp complex) was analyzed by FIT.

Results: The estimated DA of one-sample testing for Hb in the screening setting had a very low sensitivity (SE) (12.5%; 95%CI=12.3-12.7) for adenomas, with AUC=0.560 (for CRC, AUC=0.950). Testing three samples for Hb improved SE to 19.4% (95%CI=19.1-19.7%) but had little effect on overall DA (AUC=0.590). For adenomas, one-sample testing for Hb and Hb/Hp complex provided higher SE than three-sample testing for Hb (SE 20.6%; 95%CI=20.3-21.0), and the best SE was reached when two samples were tested for Hb and Hb/Hp complex (SE 47.5%; 95%CI=46.9-48.1%) (AUC=0.730).

Conclusion: The strategy of the current CRC screening could be significantly improved by testing two consecutive samples by Hb and Hb/Hp complex, instead of stand-alone Hb testing of one sample.