Aim: Colon cancer, accounting for almost 10% of all cancers in both genders worldwide, is the fourth most common cause of cancer-related deaths. Approximately 95% of cases are originated from adenomas. In recent years, early detection of colon-borne pathologies and precancerous changes have contributed to decreased mortality rates. Therefore, early diagnosis is necessary to prevent and treat colorectal cancer properly. We aimed to evaluate the correlation of fecal occult blood tests (FOBT) with different detection limits with colonoscopy results and the performance of the tests.

Material and Methods: The consistency of 3 different immunochemical FOBT (iFOBT) with cutoff values of 10, 30, and 50 ng/mL, which were used in a tertiary university hospital laboratory at different time periods, with colonoscopy results were analyzed retrospectively. The sensitivity, specificity, positive and negative predictive values of tests determined for adenoma-adenocarcinoma, advanced neoplasia, adenocarcinoma.

Results: We observed that as the cutoff values of FOBT increased, lesion detection rates decreased; 1/23, 5/22, 1/1 of the adenocarcinoma cases were not detected for the tests with detection limits of 10, 30, 50 ng/mL, respectively. The negative predictive values of the tests were above 97% for adenocarcinoma detection.

Conclusion: Changing the detection limit of the FOBT affects performance. Lowering the detection limit will facilitate the detection of adenocarcinoma patients and increase the number of colonoscopies performed due to false positive results.