Faecal Immunochemical Test

The Faecal Immunochemical Test “FIT” is a stool test used with the bowel cancer screening test.  The Faecal Immunochemical Test (FIT) uses antibodies that specifically recognise human haemoglobin (Hb). It means that a FIT result is not influenced by the presence of other blood in stools and therefore reduces the chance of false positive results.

The FIT test is used to detect and can quantify the amount of human blood in a single stool sample. A positive FIT result suggests that there may be bleeding within the gastrointestinal tract that requires further investigation. Those with a positive result are then invited for further testing, normally colonoscopy.

The Faecal Immunochemical Test measures the amount of human haemoglobin from red blood cells in micrograms per gram of faeces. The definition of a positive or negative stool test result is decided upon by the area carrying out the actual test. The lower the threshold or cut-off level that they set then the more sensitive the test will be and the more cases of cancer and adenoma they will detect. If more cases are detected then ultimately more deaths from bowel cancer will be averted.

In Scotland, FIT was introduced with a cut-off level of 80μg/g. This has a higher detection rate for advanced adenomas but a comparable cancer detection rate to gFOBT screening.

In England, FIT has been introduced with a cut-off level of 120 μg/g. However, to optimise FIT, there are plans to reduce this sensitivity threshold.

In Wales, FIT has been introduced with a cut-off level of 150μg/g. The Welsh Government have announced that the Bowel Screening Wales programme will reduce the FIT cut-off to 80μg/g by 2023.

The use of the faecal immunochemical test FIT in bowel cancer screening in the UK has indicated an improved participation from those doing the test.
Part of the reason for this improved participation might be that FIT only needs one stool sample whereas FOBT needs three.

In Scotland the proportion of those completing the bowel cancer screening test has increased from 56.2% to 64.1% for comparable 18-month periods before and after the introduction of FIT. The increase in uptake after the introduction of FIT was greatest among people from more deprived areas.

It should be noted that Scotland did include new simplified instructions on how to complete the FIT test that were not included with the older FOBT test.

Making the collection of a stool sample as simple as possible by moving from three samples to one and including some instructions obviously leads to higher participation in the bowel cancer screening test and the inclusion of HyStool as part of any collection kit would only increase that participation further.