Faecal immunochemical tests for colorectal cancer screening
Various methods of bowel cancer screening are widely used. These include colonoscopy and faecal immunological tests (FIT).
Colonoscopy is a visual examination of the intestinal mucosa for abnormalities (growths, small tumours, etc.). The patient's bowel must be emptied for this examination, which is why certain foods must be avoided in preparation and a special laxative drinking solution must be taken. During the examination, a colonoscope - a flexible tube with a light source and camera - is inserted through the rectum and colon, step by step up to the small intestine. Abnormalities, e.g. polyps, can usually be removed directly and then examined in the laboratory.
An alternative option to colorectal cancer screening is a faecal immunological test. This test uses specific antibodies to quantitatively detect human haemoglobin in stool samples. Haemoglobin is a component of blood. Small amounts of blood in stool samples are not visible to the naked eye. In this case, it is called occult blood. If the amount of occult blood exceeds a certain value, this indicates bleeding in the gastrointestinal tract. These bleedings can come from polyps (pre-cancerous bowel lesions) or from tumours in an early stage of the disease, without any other symptoms being noticeable. The FIT is characterised by a very high accuracy. In addition, there are no interactions with food components. The combination of FIT with the quantitative detection of the haemoglobin-haptoglobin complex leads to even more sensitive colorectal cancer screening (Sieg et al. 1999, Lüthgens et al. 1988). Haemoglobin is stabilised by haptoglobin during the intestinal passage, which makes bleeding of the upper intestinal tract easier to detect with the help of the complex. However, elevated levels of occult blood in the stool can also be caused by haemorrhoids or inflammation in the intestine. Therefore, in case of a positive FIT, further diagnostic tests (e.g. colonoscopy) are performed to make a final diagnosis.
In contrast to colonoscopy, FIT is a non-invasive way of screening for bowel cancer. Since no instruments have to be inserted into the body, the risk of tissue injury can be excluded. This can lead to a higher acceptance in the population and thus to higher participation rates in prevention services. In addition, patients who have already tested positive for FIT can be prioritised for colonoscopy appointments (Zorzi et al. 2018), as colonoscopy capacity is limited worldwide.
In Germany, women and men between the ages of 50 and 54 are entitled to an occult blood test once a year if they have not yet had a colonoscopy in that year. From the age of 55, it is possible to have a FIT test every two years. The costs incurred are borne by the health insurance funds.
Conclusion
- Regular colorectal cancer screening can reduce the number of colorectal cancer cases and mortality rate (Brenner et al. 2014).
- FIT tests are a sensitive, non-invasive colorectal cancer screening method that can detect colorectal cancer even in its early stages.
- More and more studies confirm the effectiveness of FIT testing, which is why it is paid for by health insurance companies in Germany from the age of 50.