Efficacy of Fecal Immunochemical Test Using Digital Rectal Exam

Fecal immunochemical testing (FIT) is an FDA-approved stool-based screening test for colorectal cancer. It offers a less invasive colorectal cancer screening option for patients who are not agreeable to colonoscopy and measures the level of Ab-globin complexes in the stool without direct interference with diet or medications. FIT has been shown to be selective for colorectal bleeding, as globin from the upper GI tract is digested by proteolytic enzymes. A meta-analysis of studies analyzing FIT showed a pooled sensitivity of 0.79 (95% CI 0.69-0.86) and specificity was 0.94 (CI 0.92-0.95). In a large study comparing FIT with another stool-based screening test, gFOBT, sensitivity of FIT was found to be 0.53-0.73 for CRC and 0.20-0.25 for advanced neoplasia compared to gFOBT, which showed 33.3% for CRC and 8.6% for advanced neoplasia. In addition, FIT requires fewer stool samples and the lack of dietary or medication modifications. As a result, compliance is likely to be higher, which is crucial for cancer detection.

A challenge inherent to stool-based screening tests is compliance with sample submission by the patients. FIT is meant to improve logistical barriers to screening because only one sample is needed, however, compliance rates with standard of care FIT (FIT-SOC) is approximately 50%. FIT using stool from a digital rectal exam (DRE) performed during a clinic visit may be an effective screening tool for patients preferring stool-based screening. FIT has been FDA-approved for the testing of spontaneously passed stool, as well as stool collected by DRE. Manufacturers of FIT have claimed that DRE provides a sufficient amount of stool for sampling, however, there are no validated studies to our knowledge which demonstrate adequate efficacy. As a result, FIT using DRE is not commonly done in clinical practice. This study aims to assess the correlation of FIT using DRE (FIT-DRE) with standard of care FIT (FIT-SOC) as a method of obtaining stool samples.