Introduction of the Faecal Immunochemical Test (FIT)

Graphic of FIT kit

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Bowel cancer screening reduces bowel cancer mortality. Since bowel cancer screening began in the UK, it has made use of a certain type of faecal occult blood test - a guaiac-based test (gFOBT). Now, the guaiac test is being replaced by a Faecal Immunochemical Test (FIT) test.

Here you can find information on the new test, it’s implementation and how this will affect healthcare professionals, people invited for screening, and patients.

FIT stands for Faecal Immunochemical Test. It is a type of faecal occult blood test which uses antibodies that specifically recognise human haemoglobin (Hb). It is used to detect, and can quantify, the amount of human blood in a single stool sample. An abnormal result suggests that there may be bleeding within the gastrointestinal tract that requires further investigation. Those with an abnormal result are then invited for further testing via a colonoscopy.

The bowel screening programme is intended for people without any signs or symptoms suggestive of bowel cancer.

In Scotland, FIT replaced guaiac Faecal Occult Blood testing (gFOBt) as the test for bowel screening in November 2017.

In England, the change is expected to happen in Spring/Summer 2019.

In Wales FIT started to replace gFOBt through a phased roll out, with 1 in 28 people receiving the new kit from the end of January 2019. Northern Ireland are yet to make a formal commitment to introduce FIT to their bowel screening programme.

The launch process will be carefully managed. Patients who are invited to take part in screening in the run up to launch won’t be able to transition to FIT until their screening episode is closed so please encourage them to do whatever test it is that they receive.

Further details for the above countries will be shared once they are available.

FIT only detects human blood

FIT is specific to human haemoglobin, which is a significant advantage over gFOBt. It means that a FIT result is not influenced by the presence of other blood in stools, such as that ingested through diet. The guaiac test is not specific to human blood – it detects the haem element of haemoglobin, which is common to all blood sources.

FIT is associated with higher uptake

There have been pilots investigating the use of FIT in eligible participants. These have reported a higher uptake in those invited, compared to that seen with gFOBt. These increases have been noted across demographics, including in men and in lower socioeconomic groups.

In a study looking at use of FIT in Scotland, it was found that overall uptake was 58.7% for FIT, significantly greater than the 53.9% for gFOBT. In the FIT pilot carried out in 2 of the 5 English hubs, uptake was 66.4% for FIT compared to 59.3% for gFOBT.

It is not clear exactly what is driving this increase but there are likely to be a range of factors including that FIT needs only one sample of poo, compared with six required for gFOBT (two samples from three separate stools). Not having to store a kit with faecal samples for several days may also remove a barrier to participation. Based on the pilot results, it is anticipated that there will be an increase in uptake with the introduction of FIT into the bowel screening programme.

FIT provides an objective, numerical result and the option to shift sensitivity

FIT uses an automatic analysis process (a machine analyser generates numerical results) whereas gFOBT requires a subjective human judgement of a colour change. This should reduce room for error in the measurement/interpretation of a result.

FIT measures micrograms of human haemoglobin per gram of faeces. What is considered to be a normal or an abnormal result can be changed by altering the numerical FIT threshold. As a general statement, the lower the threshold, the more sensitive the test will be and the more cases of cancer and adenoma that will be detected (more referrals), and ultimately deaths from bowel cancer averted. At a lower threshold there will also be more colonoscopies where no abnormalities are detected.

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

In Wales, FIT has been introduced with a threshold of 150μg/g. The Welsh Government have requested that the Bowel screening Wales programme will increase the sensitivity of FIT to 80μg/g by 2023.

As with gFOBT bowel screening, GPs of eligible patients will be notified as to whether a person has had a normal or an abnormal bowel screening result. They will not be given the numerical value of the FIT result.

Even in patients with a normal FIT screening result, it is important that GPs continue to be alert to the possibility of bowel cancer as some cancers may still be missed. GPs should also remind people to be aware of key signs and symptoms of bowel cancer, and to seek medical advice if they notice anything new or unusual, even if they’ve recently taken part in bowel screening.

Furthermore, it is important that GPs are aware that bowel screening is still indicated for eligible patients, regardless of any previous use of FIT as a symptomatic test, such as that outlined in NICE guidence DG30.

​While the switch to FIT is likely to help increase uptake by a similar level as that seen in the pilots, healthcare professionals also have an important role in supporting bowel cancer screening.

As you may be aware, bowel cancer screening has harms as well as benefits so it’s important to assist patients in making an informed decision about whether to take part. Some harms your patients should be aware of include false positives and negatives, over-reassurance following a normal result and the risks associated with follow-up colonoscopy.

GP Practices can help patients make an informed decision about participating in bowel screening. You can:

  • Ensure patient address details are up to date so that everyone gets their invitations and kits
  • Ask your Bowel Screening Centre/Bowel screening Hub for a list of eligible patients, to follow up with non-responders or first-timer patients who may not have accessed bowel screening to date
  • Talk to eligible patients about the bowel cancer screening test opportunistically within consultations
  • Encourage patients to read the information that comes with their kit so that they can understand more about the role of screening in detecting bowel cancer early and make a decision about whether to take part
  • Break down practical barriers by explaining how to do the test by using our infographic. People who have not wanted to take part before may be pleased to hear that the process is simpler with FIT than with the guaiac test
  • Answer patients’ questions and concerns about bowel cancer screening and their result
  • Keep an eye on patients who have received abnormal results and ensure there aren’t any barriers to them taking part in the colonoscopy/further investigations
  • Remind patients that bowel screening works better if people take part each time they’re invited, even if previous results have been normal

Research shows that primary care interventions can significantly increase uptake. Your GP Good Practice Guide offers practical advice to support GP Practices to endorse bowel cancer screening.

FIT may also be used as an investigation in the diagnosis of colorectal cancer in certain symptomatic patients. 

The current national guidance for FIT testing in low risk symptomatic patients is contained in NICE DG30. It recommends the use of FIT in primary care to guide referral for suspected colorectal cancer in patients without rectal bleeding, who have unexplained symptoms, but do not meet the criteria for a suspected cancer referral pathway (amounting to a risk of cancer less than 3%). This should form the basis of local defined policy.

The purpose of the FIT is to help identify patients who may have adverse bowel pathology who require colonoscopy or CT colonography. However, not all patients with colorectal cancer will have an abnormal FIT result and symptoms which indicate use of FIT may also reflect other types of cancer; so persisting symptoms would still require further management investigation. 

For symptomatic patients falling into the defined higher risk groups (warranting 2ww referral in NICE guidelines), FIT is not currently nationally recommended, and so referral under 2ww is appropriate. There are research projects looking at this now, which will provide valuable evidence on this topic. In the meantime, cancer alliances in England have been advised by NHS England to prioritise the full implementation of DG30.