GI Investigations · Patient Guide
The FIT Test: What a Positive (or Negative) Result Really Means
The FIT stool test finds invisible traces of blood. It's an excellent triage tool — and widely misunderstood in both directions.
FIT — the faecal immunochemical test — detects microscopic amounts of blood in a single stool sample. It underpins the NHS bowel screening programme and is increasingly used by GPs to triage bowel symptoms. Used well, it's a genuinely powerful test. Misread, it produces both false reassurance and unnecessary alarm.
What FIT does and doesn't measure
FIT measures human haemoglobin in stool. A positive result means blood is present — it does not say where from or why; piles, polyps, inflammation and cancers can all cause it. A negative result makes significant bowel disease much less likely but does not make it impossible, particularly if symptoms are ongoing.
When this test is usually indicated
- Routine NHS bowel screening from age 50, every two years
- GP triage of lower-risk bowel symptoms to decide who needs urgent referral
- As part of the initial work-up of a change in bowel habit
- Re-testing within screening after a previous normal round
When it may not be the right test
- Visible rectal bleeding — the blood is already proven; the question is its source, which FIT cannot answer
- Iron-deficiency anaemia — direct investigation is required regardless of the FIT result
- As a substitute for colonoscopy when symptoms are significant or persistent
- Reassurance in the face of ongoing symptoms after a single negative test
Think of FIT as a filter, not a verdict. A positive result needs colonoscopy; ongoing significant symptoms need assessment even with a negative result. Its job is to help decide who needs the camera first.
What happens if you do need it
A positive FIT is followed by colonoscopy to find the source of the blood — most positives turn out to be benign causes, but the examination is what proves it. Privately, that colonoscopy can usually be arranged within days rather than weeks. Mr Papettas is JAG dual-accredited, with polyp removal performed at the same examination whenever needed.
Frequently asked questions
Does a positive FIT test mean I have cancer?
No — most positive results are due to benign causes such as polyps, piles or inflammation. But it always warrants a colonoscopy, because that's how the minority of serious causes are found early.
Can I skip the colonoscopy if I feel well after a positive FIT?
Feeling well doesn't change the finding — invisible blood has a source, and early-stage disease is typically symptomless. This is exactly the scenario colonoscopy exists for.
Is a negative FIT a guarantee?
No test is. A negative FIT makes serious disease much less likely at that moment, but symptoms that continue or return still need assessment.
How accurate is FIT?
Very good at what it does — detecting blood. Its limitation is that some lesions bleed intermittently or not at all, which is why symptoms still matter.
What FIT threshold triggers referral?
Thresholds vary by pathway; screening and symptomatic services use different cut-offs. Your result letter or GP will state whether yours requires referral.
How quickly can I get a colonoscopy after a positive FIT privately?
Usually within days of consultation at Nuffield Health Warwickshire — call 01926 935121.
Related reading
Unsure whether you need this test?
Mr Trif Papettas FRCS is a Consultant Colorectal and General Surgeon at Nuffield Health Warwickshire Hospital, Leamington Spa, and a JAG dual-accredited endoscopist. A consultation settles which investigation, if any, your symptoms actually need — and if a test is indicated, it can usually be arranged within days.
Self-referrals welcome · No GP letter required · Self-pay and insured patients seen at Nuffield Health Warwickshire Hospital, Leamington Spa CV32 6RW