Critical considerations of fecal occult blood tests for colorectal cancer

Abstract

1University of Dundee, Nethergate, Dundee, DD1 4HN, Scotland, UK *Author for correspondence: r.j.c.steele@dundee.ac.uk The most commonly used strategy in colo­ rectal cancer (CRC) screening pro grams involves the use of stool tests to detect occult blood, and guaiac fecal occult blood tests (gFOBTs) are, to date, the only fecal tests shown to reduce CRC mortality in population­based randomized trials [1]. However, gFOBTs also carry disadvantages. A major concern is that interval cancers account for around 50% of cancers detected in gFOBT screened populations [2] and recent data show that gFOBTs are less sensitive in women than in men, and in both rectal and right­sided cancers when compared with left­sided disease [2,3]. In addition, the test is associated with a high false­positive rate with no neoplasia detected in around half of colonoscopies performed following a positive gFOBT [2,3]. This may be, in part, explained by the fact that gFOBTs are not specific for human hemoglobin (Hb) and are subject to possible dietary interference from, for example, red meat and high­peroxidase fruits and vegetables. As a result, it has been common practice to instruct participants to adhere to dietary restrictions ahead of sample collection, although this may act as a barrier to screening and affect participation rates [4]. However, data from a meta­analysis did not support dietary restrictions with gFOBTs, leading to recommendations that restrictions are abandoned to improve adherence rates [5]. Fecal immunochemical tests (FITs) are now available and are increasingly being used in screening programs. Unlike gFOBTs, FITs are specific for the detection of human Hb, eliminating any potential for dietary interference, and are also more specific than gFOBT for lower gastrointestinal bleeding. In addition, modern FITs generally allow a more convenient method of sample collection, and are associated with better participation rates [6]. Another major advantage of FIT is that automated versions not only eliminate interobserver variability, but also the quantitative nature of these tests allow provision of a measured fecal Hb concentration. Screening program “...the adoption of fecal immunochemical tests in colorectal cancer screening programs has potential to address participation, appropriate positivity rates and the problem of false‐negative results.” EDITORIAL