Identifying the best cutoff value of the fecal occult blood immunochemical test in the detection of advanced and neoplastic colorectal lesions.

Objective: Screening is an effective tool for detecting colorectal lesions in asymptomatic subjects. There is a positive correlation between fecal immunochemical test (FIT) values and the size of tumors. Despite the efficacy of screening, the detection of colorectal cancer (CRC) remains low. The primary objective was to evaluate the best FIT cutoff value for detecting advanced adenomas and CRC among individuals at average risk in a country with a high incidence and morbidity from CRC.

Methods: This observational and prospective study analyzed consecutive cases in 1461 asymptomatic subjects with a positive FIT (≥ 100 ng hemoglobin [Hb]/mL) referred for colonoscopy (2012-2015) at a tertiary center in Uruguay.

Results: Colorectal lesions were detected in 35.3% (516/1461) of cases, with a mean age of 62.8 ± 8.3 years. About 53.2% were men and 65.1% of the tumors were located in the left side of the colon. The size of the lesion and FIT values (p = 0.001) were positively correlated. Laterally spreading tumors predominated in the right colon (586 ng Hb/mL; 95% Confidence interval [CI] 443.4-760). One hundred and thirty-five (26%) lesions were advanced adenomas (15 ± 6.7 mm); 694.6 ng/mL; 95% CI 632.4-756.9). The highest diagnostic yield (0.5112) for advanced adenomas was at a FIT level of 400 ng Hb/mL (accuracy 88.6%). There were significant differences in FIT values early and advanced CRC (927 ng/mL; [95% CI: 637-1082] vs. 1453 [95% CI: 1352-1594; p = 0.001]).

Conclusion: A FIT value of 400 ng Hb/mL was the best diagnostic yield to detect advanced adenomas and CRC. This value is useful during the COVID-19 pandemic as it allows prioritization of colonoscopy to those most at risk of significant disease, thus reducing risks to both patients and healthcare workers.