Positive FIT Test: What It Means and What Happens Next

The Faecal Immunochemical Test (FIT) has transformed how bowel symptoms are assessed in the UK. It is used in the national bowel cancer screening programme and increasingly by GPs to triage symptomatic patients. But the letter that tells you your result is positive rarely explains what that actually means — so let's do that properly.

What FIT actually measures

FIT detects tiny quantities of human haemoglobin — blood — in the stool, far below what is visible to the eye. It is specific to human blood from the lower digestive tract, which makes it more accurate than the older guaiac tests, and it is reported as a number (micrograms of haemoglobin per gram of stool) rather than simply positive or negative. Screening programmes and GPs apply different thresholds, which is why two people with "positive" results may have quite different numbers.

Does a positive FIT mean I have cancer?

Usually not. Most people with a positive FIT do not have bowel cancer. Blood in the stool has many causes: haemorrhoids, anal fissures, polyps, diverticular disease, and inflammation of the bowel lining can all produce a positive result. However, a positive FIT does identify a group in whom bowel cancer is meaningfully more likely than in the general population — and in whom polyps (the benign growths from which most bowel cancers develop) are common. That is precisely why the result must not be ignored: the higher the FIT number, and the older you are, the stronger the case for prompt investigation. Recent UK research also shows that combining the FIT value with age and iron-deficiency anaemia status identifies high-risk patients with considerable accuracy.

The next step is colonoscopy

FIT tells you that blood is present; it cannot tell you where it is coming from. A colonoscopy answers that question definitively — it examines the entire colon directly, and crucially it allows polyps to be removed during the same procedure, which is how colonoscopy prevents cancers rather than merely finding them. The quality of the examination matters: completion rate and detection rate are audited under the JAG accreditation scheme, which I explain in this guide. The practicalities and timescales of arranging one privately are covered in How Quickly Can I Get a Private Colonoscopy in Warwickshire?

How quickly should it happen?

NHS guidance aims for urgent-pathway patients to be investigated within weeks, but local waits vary, and the uncertainty itself takes a toll. Privately, a consultation and colonoscopy can usually be arranged within days. Whichever route you take, the important thing is that a positive FIT is followed by a definitive examination — not by a repeat FIT, and not by waiting to see if symptoms settle.

What if the colonoscopy is normal?

That is a genuinely reassuring outcome — a complete, high-quality colonoscopy is the best available evidence that your colon is healthy. Your surgeon will then consider whether the blood may have come from higher in the digestive tract (sometimes warranting a gastroscopy, which Mr Papettas is also JAG-accredited to perform) or from a benign anal cause such as haemorrhoids, covered in my guide to rectal bleeding.