Faecal immunochemical tests (FIT) in the assessment of patients presenting with lower bowel symptoms: Concepts and challenges.

Colonoscopy is a relatively scarce resource in many countries, including Scotland, and a simple investigation which would aid general practitioners in particular in decision-making as to which patients presenting with lower bowel symptoms warranted referral would be of much help. Faecal immunochemical tests for haemoglobin (FIT) have many advantageous characteristics and are now proven to be of considerable value in the timely assessment of patients with symptoms of lower bowel disease. Quantitative FIT provide numerical estimates of faecal haemoglobin concentration (f-Hb) and, at low f-Hb cut-off, FIT have high sensitivity for colorectal cancer (CRC) and could be used as a rule-in test to stimulate rapid referral, especially when symptoms are suggestive of serious bowel disease. Perhaps more importantly, a low f-Hb gives considerable reassurance that significant bowel disease (CRC + higher-risk adenoma + inflammatory bowel disease) is absent and further investigation may not be warranted: however, no test is perfect, so some cases will remain undetected using FIT alone and robust safety netting is required, possibly including watching and waiting, referral to clinics in secondary care, or a repeat FIT. Moreover, the FIT results should not be taken in isolation, but clinical impressions and the results of other investigations, probably including the full blood count, should be considered. Challenges still exist, however, and harmonisation of aspects of the available FIT analytical systems is required. Moreover, a number of seemingly valid clinical concerns remain and these require resolution through further research and reporting of studies done in real clinical practice.