01Purpose and principlesWhat the assessment is for and the core concepts behind it.
Quantitative FIT measures human haemoglobin in stool and reports a concentration in micrograms per gram of faeces. NICE recommends it for adults of any age with an abdominal mass, change in bowel habit or iron-deficiency anaemia; age 40 or over with unexplained weight loss and abdominal pain; age under 50 with rectal bleeding plus unexplained abdominal pain or weight loss; age 50 or over with unexplained rectal bleeding, abdominal pain or weight loss; and age 60 or over with anaemia even when iron deficiency is not shown.
FIT remains indicated when a symptomatic person previously had a negative screening FIT because screening addressed an earlier asymptomatic time point. At least 10 micrograms haemoglobin per gram supports suspected colorectal-cancer referral. A rectal mass, unexplained anal mass or anal ulceration bypasses waiting for FIT, while below-threshold results need active review of persistent symptoms and clinical concern.
Key points
- Offer symptomatic FIT to adults of any age with an abdominal mass, change in bowel habit or iron-deficiency anaemia.
- Also offer it from age 40 with unexplained weight loss plus abdominal pain, and under age 50 when rectal bleeding accompanies either unexplained abdominal pain or weight loss.
- Offer FIT from age 50 with unexplained rectal bleeding, abdominal pain or weight loss, and from age 60 with anaemia even without proven iron deficiency.
- A previous negative screening FIT does not replace a new symptomatic FIT and clinical assessment.
- Refer at 10 micrograms haemoglobin per gram or above; lower values require review when symptoms persist.
- Refer a rectal mass, unexplained anal mass or anal ulceration without waiting for FIT.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
FIT is specific for human globin and mainly detects lower gastrointestinal bleeding because globin is degraded during upper-GI transit.
NICE recommends FIT for adults with specified symptoms and findings, including change in bowel habit, iron-deficiency anaemia and defined rectal-bleeding groups.
A threshold of at least 10 micrograms haemoglobin per gram of faeces is used in NICE HTG690 to guide suspected colorectal-cancer pathway referral.
Below-threshold cancer risk is lower, not zero; non-returned samples, persistent symptoms and discordant clinical findings need active safety-netting.
Visible rectal bleeding is not a reason to withhold FIT within the recommended symptomatic pathway because intermittent tumour bleeding may still be detected quantitatively.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Quantitative FIT sampleFirst step - Why
- measure faecal haemoglobin concentration for risk stratification
- Interpretation and limitations
- Use the numerical value and assay reporting limit; positive and negative labels conceal information near the threshold.
- 02
Full blood count and ferritin - Why
- identify anaemia and iron depletion that alter urgency and the need for gastrointestinal investigation
- Interpretation and limitations
- Iron deficiency can coexist with a low FIT and should not be dismissed as explained until its source has been assessed.
- 03
Abdominal and digital rectal examination - Why
- identify masses, obstruction, anorectal disease and alternative explanations
- Interpretation and limitations
- A rectal mass overrides reliance on FIT; a benign anorectal finding does not necessarily explain other alarm features.
- 04
Repeat clinical review after a result below threshold - Why
- determine whether symptoms are resolving, persisting or progressing
- Interpretation and limitations
- Escalate persistent unexplained symptoms through local pathways rather than repeatedly using FIT as a substitute for diagnosis.
- 05
Colonoscopy or CT colonography after referral - Why
- identify and characterise structural colorectal disease
- Interpretation and limitations
- FIT selects risk; it does not localise, biopsy or exclude pathology such as non-bleeding polyps.
04Clinical next stepsHow the result changes management or prompts escalation.
01Worked case: applied faecal immunochemical testing in symptomatic adultsReach a specific decision and confirm it happenedFirst stepA 71-year-old has an unexplained change in bowel habit, no palpable rectal mass and stable observations. The clinician plans quantitative FIT and must interpret the eventual numerical result against the current NICE referral threshold.+
- 1Confirm stable observations and absence of obstruction or a palpable mass, then record the exact NICE symptom indication before issuing the kit.
- 2Explain single-sample collection, avoiding contamination and returning the device promptly; create a task so a missing sample is actively chased.
- 3The laboratory reports 22 micrograms haemoglobin per gram of faeces. Check that this exceeds the current NICE referral threshold of 10 micrograms per gram.
- 4Refer the patient on the suspected colorectal-cancer pathway, including symptom duration, examination, blood results and the quantitative FIT value in the referral.
- 5The outcome is urgent colorectal assessment. Verify referral acceptance and subsequent structural investigation and histology; do not close the episode merely because symptoms fluctuate.
02Below-threshold symptomatic reviewSafety-net a low result against the continuing clinical pictureA 52-year-old with unexplained abdominal pain and weight loss has FIT 3 micrograms per gram, normal haemoglobin and no palpable mass, but weight loss continues at four-week review.+
- 1Confirm correct sampling and the numerical result, then repeat weight, abdominal and rectal assessment and review blood count, ferritin, CRP and other indicated tests.
- 2Recognise that the low result reduces colorectal-cancer probability but does not explain progressive weight loss; follow the local safety-net pathway for further investigation or specialist advice.
- 3Verify diagnostic outcome and give an earlier trigger for bleeding, obstruction, worsening pain or a newly palpable mass rather than simply repeating FIT.
03Mass bypass pathwayRefer the examination finding without waiting for faecal haemoglobinA 59-year-old with tenesmus has a firm circumferential low rectal mass on digital examination; a recently returned FIT is 2 micrograms per gram.+
- 1Record the mass position, distance, circumferential extent and examination tolerance and check for obstruction, bleeding and physiological compromise.
- 2Submit an urgent suspected colorectal-cancer referral on the mass finding; do not repeat or reinterpret the low FIT as a rule-out test.
- 3Verify endoscopy with biopsy, pelvic MRI and systemic staging, and address progressive obstruction or major bleeding urgently while the pathway proceeds.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
- Track whether a kit was issued, returned and processed; a missing sample is an incomplete pathway rather than a negative result.
- Review the quantitative concentration with the symptom trajectory and laboratory data, documenting why referral is or is not made.
- After below-threshold FIT, provide a clear interval and trigger for reassessment of persistent bleeding, bowel-habit change, pain, weight loss or anaemia.
- Audit diagnostic outcomes and delayed presentations because FIT pathways require reliable safety-netting as well as correct thresholds.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
The number matters
A quantitative concentration conveys more information than a binary label and prevents confusion when laboratories use different reporting conventions.
Sensitivity is not certainty
Some colorectal cancers shed little blood or bleed intermittently, so a low result reduces probability without eliminating disease.
Sampling is part of the test
Failure to return or correctly collect a specimen must be noticed and addressed; it cannot be silently coded as reassuring.
Clinical discordance deserves action
A palpable mass or worsening alarm pattern has greater consequence than a single low faecal haemoglobin measurement.
07Common pitfallsFrequent interpretation and management errors.
- 01
Calling an unreturned kit FIT negative creates false reassurance and loses a symptomatic patient from the pathway.
- 02
Repeating below-threshold FIT indefinitely instead of reassessing persistent symptoms delays definitive investigation.
- 03
Using serum tumour markers as a substitute for quantitative FIT or structural investigation is not supported for initial diagnosis.
- 04
Failing to document who will review the result leaves a high-value triage test without an accountable decision.