Distinguishing FIT in Screening from FIT in Assessment of the Symptomatic
||FIT in Screening
||FIT in the Symptomatic
||Asymptomatic individuals eligible to participate in structured screening programmes, which differ from nation to nation in the UK along with those older individuals who choose to “opt-in”.
||Patients of any age who present in primary care with lower abdominal symptoms such as rectal bleeding, a change in bowel habit to constipation or diarrhoea, unexplained weight loss, anaemia, abdominal pain, and abdominal or rectal mass. In addition, some patients seen at certain secondary care clinics such as gastroenterology, will benefit.
||To select those participants in screening programmes who have no symptoms, but are at highest risk of colorectal neoplasia – cancer and higher-risk (advanced) adenoma.
||To identify those patients who are most unlikely to have significant colorectal disease and would not benefit from referral for colonoscopy, saving resources and shortening waiting times, as well as identifying those who have significant colorectal disease and would benefit.
||Rule in neoplasia.
||Rule out significant colorectal disease (cancer + higher-risk adenoma + inflammatory bowel disease).
Rule in significant colorectal disease.
|Faecal Haemoglobin Cut-off Concentration Used
||High – especially in colonoscopy constrained countries. Selected to give the screening programme performance characteristics desired, such as the positivity rate with which the available colonoscopy resource could cope.
||Low – 10 µg Hb/g faeces is widely recommended – selected to ensure that patients with “negative” results, most unlikely to have significant colorectal disease, do not necessarily get early referral for colonoscopy. And, if “positive”, stimulates early referral to secondary care for further investigation.
|Interpretation of Results
||A “positive” result means that a risk of significant colorectal disease is present and further investigation is warranted. A “negative” result means the participant should be invited again at the set screening interval.
||If the result is “negative”, there is considerable reassurance that significant colorectal disease is not present. A “detectable” faecal haemoglobin means that the patient warrants further investigation.
||Not all colorectal neoplasia is detected – interval cancer proportions are high when high faecal haemoglobin cut-offs are applied. Thus, a “negative” result does not mean that colorectal neoplasia is absent and participants receive information on lifestyle and symptoms. There is a “reassurance” effect of a “negative” result. Moreover, a “positive” result does not mean that colorectal neoplasia is present, but the participant may undergo an invasive and potentially harmful investigation.
||FIT in assessment of the symptomatic is not perfect and some colorectal disease will be missed if a “negative” result is used as guidance for no referral. Most cancers are detected, but a slightly greater proportion of higher-risk adenoma and inflammatory bowel diseases are not detected. Thus, patients with “negative” results could be given reassurance, but possible alternatives such as watching and waiting, referral to secondary care clinics, or a repeat FIT might be warranted, particularly if symptoms persist.
||Not only cancer detected but also some higher-risk adenoma, sometimes precursors of cancer, and inflammatory bowel disease.
||Not only possibility of significant colorectal disease being “excluded”, but cancer, higher-risk adenoma, sometimes precursors of cancer, and inflammatory bowel disease detected.
||As FIT screening progresses and as the available colonoscopy resource expands, implementation of lower cut-offs over time would increase detection of cancer and even more higher-risk adenoma.
||Investigation of more analytically sensitive methods for detection of faecal haemoglobin, since many patients have undetectable faecal haemoglobin with current methodology. Use of FIT result in combination with other variables such as blood haemoglobin.