Small Bowel Evaluation in Asymptomatic Fecal Immunochemical Test-Positive Patients with a Negative Colonoscopy: Is It Necessary?

Abstract

Screening for colorectal cancer (CRC) and its precursors by fecal occult blood test (FOBT) is widely recommended and is being applied more than ever [1–3]. Although annual or biennial guaiac fecal occult blood test (gFOBT) screening has been proved to reduce the mortality of CRC [4], the gFOBT has been faulted for its low sensitivity [5, 6]. More recently, the fecal immunochemical test (FIT) has been introduced as an alternative to the gFOBT. The FIT is currently preferred over the gFOBT due to its higher sensitivity and improved detection rate for advanced neoplasia [5, 7–10]. Besides its diagnostic performance, the FIT has several advantages over the gFOBT including no need for dietary restriction, easier stool collection method, and automated analysis [11]. Furthermore, quantitative FIT allows for the adjustment of the cutoff value for an abnormal result based on population characteristics and available colonoscopy resources. Due to these characteristics, quantitative FIT is more favored as a screening tool than qualitative FIT [11]. The FIT selectively reacts with the globin moiety of human hemoglobin [12]. Because globin is rapidly degraded by proteases in the upper gastrointestinal (GI) tract, the FIT dose not detect small amounts of blood in the upper GI tract and selectively recognizes occult bleeding of colorectal origin [12]. With regard to small bowel lesions, although there is a possibility that some small bowel occult bleeding could be identified by FIT, no data are currently available regarding this issue. In the current issue of Digestive Diseases and Sciences, Chiba et al. [13] present the results of their prospective study on small bowel evaluation in asymptomatic FIT-positive subjects with a negative colonoscopy. In this, the first study to evaluate the small bowel with capsule endoscopy (CE) in asymptomatic FIT-positive patients with a negative colonoscopy, 53 asymptomatic patients with FIT-positivity and a negative total colonoscopy and esophagogastroduodenoscopy underwent CE. The CE findings were classified into three categories: P0, no abnormalities or findings without potential for bleeding; P1, findings with uncertain potential for bleeding; and P2, findings with high potential for bleeding. The cecal completion rate was 92.5%. There were no cases of P2, 19 cases of P1, and 34 cases of P0. Moreover, no abnormalities were identified in five patients who underwent additional diagnostic evaluations that were considered necessary based on the individual clinical results. No clinically significant small bowel lesions were found in the asymptomatic FIT-positive patients with negative bidirectional endoscopy. Although FIT has been widely accepted as a CRC screening tool, 40–60% of subjects with a positive FIT are found to have no lesions in their colon or rectum to explain their positive status [5, 14, 15]. How then do we explain the discrepancy between the results of FIT and colonoscopy? There are several possible explanations for this discrepancy. First, this may reflect true false-positive results of FIT for advanced neoplasia. Quantitative FIT results are subjected to predetermined cut-off values for fecal hemoglobin; this methodology could inevitably yield some true false positives. Additionally, medications that can increase the likelihood of GI bleeding may cause false-positive FIT J. J. Park Department of Internal Medicine, Kyung Hee University Hospital at Gangdong, Kyung Hee University, Seoul, Korea