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
FIT measures traces of human blood in stool that are invisible to the eye. Research on FIT centres on colorectal cancer, the second most common cause of cancer death worldwide, with nearly 900,000 deaths a year. Most colorectal cancers develop slowly, over 10–15 years, from polyps in the bowel lining; five-year survival is above 90% at stage I and below 15% at stage IV. FIT is supported by multiple large randomised trials and is used in national screening programmes in the UK, Europe, Australia, and Asia, where a positive result is followed up with colonoscopy. Research also reports that combining FIT with stool M2-PK, which measures a different signal, identifies more cancers than either test alone. FIT is not diagnostic on its own.
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 — in screening programmes, a result above it is followed up with colonoscopy. 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)
Below the laboratory's positivity threshold. A negative FIT does not rule out colorectal cancer — studies report about 20–25% of colorectal cancers test negative on any single annual FIT. Symptoms such as rectal bleeding, a change in bowel habit, or unexplained iron deficiency should be discussed with a registered medical practitioner regardless of the result.
National Institute for Health and Care Excellence (NICE), Colorectal Cancer Guideline, 2020
Positive
≥ 10 μg Hb/g faeces (threshold varies by programme)
Above the laboratory's positivity threshold. In published screening programmes, about 5–10% of positive FITs led to a colorectal cancer finding, and a further 30–40% to polyps. A positive FIT is not diagnostic — screening programmes follow it up with further investigation. Discuss with a registered medical practitioner.
Moss S et al., The Lancet, 2012 — doi:10.1016/S0140-6736(12)60838-9
This page summarises published research for general education. It is not medical advice and does not interpret individual results. Discuss your results with a registered medical practitioner.
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.