I am 71 years old and have enjoyed reasonably good health all my life, although osteoarthritis of the knees and cataracts are now two of the joys of growing older. I have taken part in the Scottish Bowel Screening Programme every two years since the first pilot back in 2000. These are facts. The following story is fictional, but the scenario is likely to become a real conundrum for many in the not too distant future.
Imagine my pleasure when I was invited again for bowel screening and received a small, simple to use, hygienic specimen collection device which needed only one sample of my faeces. Following the pictorial instructions, I completed the test and posted it back to the Screening Centre. I learned that the new test was called a faecal immunochemical test for haemoglobin, commonly known as a FIT. I learned that FIT have many advantages over traditional card-based guaiac faecal occult blood tests  and are being rolled out across the UK for screening.  I was relieved to receive a letter within a few days telling me that I had a negative test result, although that did not mean I did not have cancer, and to watch out for symptoms.
Unfortunately, a few months later, I did notice that my bowel motions were very dark in colour and the frequency with which I had to pass rather loose bowel motions had increased substantially. So, following the advice in the letter that I received from the Screening Programme, and had heard and read very often in the media, I went to my GP, who noted my symptoms and gave me a FIT device. I competed this and took it back to the surgery for onward transmission to the local laboratory for analysis. Three days later, I got a phone call from the hospital endoscopy department telling me that I had a very abnormal result and that an appointment for a colonoscopy had been made for me later that week. Cancer surely does not develop so quickly, I thought. Why were the two FIT results so different? I was very confused.
Unfortunately, the mass media seem very confused too, and recent reports [3,4,5] completely mix up many aspects of FIT in screening and FIT in assessment of patients with symptoms. It is important for everyone to realise that FIT is one test, but it is used very differently in two very dissimilar clinical applications (and possibly more in the future).
Firstly, FIT is used in screening. Screening is the assessment of apparently healthy people who do NOT have any symptoms. Everyone in the country who is eligible to participate gets an invite. The aim is to pick out those individuals who are at the highest risk of having colorectal cancer (and incidentally finding high risk adenoma, sometimes precursors of cancer, and severe inflammatory bowel disease). The faecal haemoglobin concentration threshold (cut-off) that is used as the criterion for referral for further investigation has to be set quite high so that only a few percent of participants are called for colonoscopy, which is a scarce resource. FIT are the best available non-invasive test for screening, but a positive FIT result does not mean that cancer is present and a negative FIT result does not mean that cancer is absent.
Secondly, FIT are also becoming widely used in assessment of patients who, in contrast, do have symptoms of lower abdominal disease. Such symptoms are common, although significant colorectal disease is much rarer In this clinical setting, because the aim is to dissect out those patients with symptoms who are likely to have disease and will benefit most from colonoscopy, the cut-off for referral is set at the lowest possible concentration. A positive FIT result does not always mean that significant bowel disease is present, but it does mean that further investigation is warranted. A negative FIT result, however, is very reassuring that significant bowel disease is not present and investigation may not be needed. FIT, like all investigations, are not perfect, however, and further investigation is warranted if symptoms persist.
Thus, FIT provides one investigation but which is used in two very different clinical settings, with different aims, different cut-offs, different outcomes, different benefits and different harms. It seems hardly surprising that many are confused. It is up to us as healthcare professionals involved in screening and assessment of patients, the media, the bowel cancer charities and others, to attempt to clarify potential misunderstandings in as many ways as possible as FIT are rolled out across the UK for both clinical purposes.