This question comes up constantly, and the answer has changed. If you were told a few years ago that there is no point testing when you can already see blood, that advice is out of date.
The old assumption
The reasoning seemed sound. FIT looks for blood in stool. If someone can see blood in the toilet, of course the test will be positive. It will be positive in everyone with haemorrhoids, everyone with a fissure, everyone with any anal cause of bleeding at all, and so it will tell you nothing useful about who needs a colonoscopy.
Early guidance reflected that logic and excluded people with rectal bleeding from FIT testing.
What the evidence showed
The assumption did not survive contact with data.
The NICE-FIT study followed nearly 10,000 people referred on an urgent suspected cancer pathway in the UK. Everyone had both a colonoscopy and a FIT test, so the test could be compared directly against what was actually found. Within that group, more than 3,000 people had rectal bleeding as one of their symptoms.
FIT did not fall apart in this group. Its sensitivity was found to be at its highest in exactly this context.
There is a physiological reason. FIT detects breakdown products of haemoglobin rather than fresh surface blood. Bleeding from a haemorrhoid or a fissure tends to sit on the surface of the stool or appear on the paper, rather than being mixed through the sample the test analyses.
Both NICE and the joint guidance from the Association of Coloproctology and the British Society of Gastroenterology now endorse using FIT in people with rectal bleeding.
What your result means if you are bleeding
If your FIT is raised, you need investigation of the whole colon. This is treated as an urgent pathway.
If your FIT is normal, the picture is more reassuring than you might expect. The authors of the NICE-FIT study noted that even at the 10 µg Hb/g threshold, the chance of colorectal cancer in someone with rectal bleeding and a negative FIT is around 0.1 to 0.2%. Following up with a routine flexible sigmoidoscopy brought that down further, to about 0.03%.
That does not mean a normal result ends the matter. Persistent or recurrent bleeding still warrants referral. What changes is the urgency and the type of investigation: it is more likely to be a routine look at the lower bowel than an urgent whole-colon examination.
The thing not to do
Do not use a normal result to talk yourself out of seeing someone.
Visible rectal bleeding deserves a conversation with a doctor regardless of what a test says. That is partly about the small residual risk, and partly because there are other things worth identifying and treating that FIT was never designed to find.
If you have noticed blood, book an appointment. A test can be part of that assessment, and often should be. It is not a replacement for it.
References
- D’Souza N, et al. Faecal immunochemical test is superior to symptoms in predicting pathology in patients with suspected colorectal cancer symptoms referred on a 2WW pathway (NICE-FIT). Colorectal Disease 2021;23(7):1630.
- Monahan KJ, Davies MM, Abulafi M, et al. Faecal immunochemical testing (FIT) in patients with signs or symptoms of suspected colorectal cancer: a joint guideline from the Association of Coloproctology of Great Britain and Ireland (ACPGBI) and the British Society of Gastroenterology (BSG). Gut 2022;71:1939 to 1962. doi:10.1136/gutjnl-2022-327985
- Saw KS, Liu C, Xu W, Varghese C, Parry S, Bissett I. Faecal immunochemical test to triage patients with possible colorectal cancer symptoms: meta-analysis. British Journal of Surgery 2022;109(2):182 to 190. doi:10.1093/bjs/znab411
- National Institute for Health and Care Excellence. Quantitative faecal immunochemical testing to guide colorectal cancer pathway referral in primary care. Diagnostics guidance DG56, 2023.
Figures are drawn from the sources above. Framing and commentary are the author’s own. Last reviewed August 2026.