FIT
Faecal Immunochemical Test
What it is
The faecal immunochemical test (FIT) detects human haemoglobin in stool using antibodies specific to the globin portion of human haemoglobin. This specificity for human haemoglobin distinguishes FIT from older guaiac-based faecal occult blood tests (gFOBT): FIT does not react to haemoglobin from dietary animal sources (red meat, fish), does not require dietary restriction before testing, and is not affected by vitamin C or aspirin — all limitations of gFOBT that reduced compliance and specificity. FIT detects haemoglobin from bleeding in the lower gastrointestinal tract — colorectal cancers, adenomatous polyps, and inflammatory conditions such as colitis and angiodysplasia. The test is administered as a home collection: a stool sample is collected using a provided kit and returned for laboratory analysis. A single annual FIT is integrated into the Blueprint Bloodwork cycle, coordinated with the rest of the annual draw.
Why we measure it
Colorectal cancer is the second most common cause of cancer death globally, responsible for nearly 900,000 deaths annually. It develops almost invariably through a well-characterised precancerous sequence — normal mucosa to adenomatous polyp to carcinoma — over a period of 10–15 years. This long precancerous window is both the biological basis for screening effectiveness and the reason it works: identifying and removing adenomas before malignant transformation prevents cancer; detecting cancer at stage I produces five-year survival rates above 90%, versus below 15% for stage IV. FIT has been validated as an effective colorectal cancer screening tool across multiple large population-based randomised trials and is used in national screening programmes in the UK, Europe, Australia, and Asia. Annual FIT enables detection of occult GI bleeding — from cancers, large polyps, or high-risk lesions — that is entirely invisible without testing. A positive FIT result triggers colonoscopy, which allows direct visualisation and removal of polyps before they become cancerous. In conjunction with M2-PK testing (which detects metabolic rather than haemorrhagic tumour signals), the two non-invasive stool tests together have higher sensitivity for colorectal cancer than either alone.
Why every 12 months
Annual FIT is the recommended frequency for population-based colorectal cancer screening programmes in most international guidelines. This reflects the biology: colorectal cancer and large polyps can develop or bleed intermittently, and annual testing minimises the window during which a lesion could grow undetected between screenings. Colonoscopy, by contrast, is typically recommended every 10 years for individuals with normal findings — FIT bridges those intervals with non-invasive annual surveillance.
What movement means
FIT results are reported as either qualitative (positive or negative at a defined haemoglobin threshold, typically 10 μg Hb/g faeces for population screening) or quantitative (haemoglobin concentration in μg/g). The clinical decision point is the positivity threshold — a result above this threshold triggers colonoscopy referral. Different screening programmes use different thresholds, balancing sensitivity (detecting more lesions) against specificity (reducing unnecessary colonoscopies).
Negative
< 10 μg Hb/g faeces (threshold varies by programme)
No significant occult haemoglobin detected. Annual retesting is appropriate. A negative FIT does not exclude colorectal cancer with certainty — approximately 20–25% of colorectal cancers will have a negative FIT on any given annual test — but substantially reduces the probability and provides reassurance. Persistent symptoms (rectal bleeding, change in bowel habit, unexplained iron deficiency) warrant clinical investigation regardless of FIT result.
National Institute for Health and Care Excellence (NICE), Colorectal Cancer Guideline, 2020
Positive
≥ 10 μg Hb/g faeces (threshold varies by programme)
Occult haemoglobin detected above the positivity threshold. Colonoscopy is recommended. Approximately 5–10% of positive FITs in screened populations will find colorectal cancer; a further 30–40% will find adenomatous polyps requiring removal. A positive FIT is not diagnostic — it is a signal that warrants colonoscopic investigation.
Moss S et al., The Lancet, 2012 — doi:10.1016/S0140-6736(12)60838-9
In the protocol
References
- 1.
Moss S, Mathews C, Day TJ, et al.. “Increased Uptake and Improved Outcomes of Bowel Cancer Screening with a Faecal Immunochemical Test: Results from a Pilot Study within the National Bowel Cancer Screening Programme.” Gut. 2017.
- 2.
Imperiale TF, Ransohoff DF, Itzkowitz SH, et al.. “Multitarget Stool DNA Testing for Colorectal-Cancer Screening.” New England Journal of Medicine. 2014.
- 3.
Allison JE, Sakoda LC, Levin TR, et al.. “Screening for Colorectal Neoplasms with New Fecal Occult Blood Tests: Update on Performance Characteristics.” Journal of the National Cancer Institute. 2007.
- 4.
Sung JJY, Ng SC, Chan FKL, et al.. “An Updated Asia Pacific Consensus Recommendations on Colorectal Cancer Screening.” Gut. 2015.