Most home bowel tests give you a word. Positive or negative. Detected or not detected. It feels clean, and it is almost useless.
FIT is a quantitative test. It produces an actual figure: the concentration of haemoglobin in your sample, in micrograms per gram. Reducing that figure to one of two words discards nearly all the information it contains.
What the range actually looks like
A rapid colorectal diagnosis service in Nottingham stratified patients by their actual FIT value and tracked how many turned out to have cancer. The results are striking:
| FIT result (µg Hb/g) | Cancer detection rate |
|---|---|
| 100 and above | 20.7% |
| 10 to 99 | 3.3% |
| 4 to 10 with abnormal blood tests | 0.6% |
| Below 4 | 0.1% |
Every one of the first two rows counts as “positive” under the UK symptomatic threshold of 10. But a person at 15 and a person at 400 are in profoundly different situations, and telling them both “your test was positive” serves neither of them.
At 20.7%, roughly one in five people needs a colonoscopy urgently. At 3.3%, investigation is still clearly warranted, but the conversation is a different one. The anxiety those two people should be carrying is not the same, and pretending otherwise is not kindness.
Why this is the direction of travel
Services around the UK are increasingly using the absolute value to decide not just whether to investigate but how quickly and by what route. Higher values go to direct rapid access. Intermediate values go through the urgent pathway. Low values with normal bloods are managed with primary care follow-up and careful safety-netting.
National guidance has not yet formalised this. NICE reviewed the evidence and concluded that a single threshold remains the most cost-effective approach for a national system right now. But the data is accumulating, and the direction is clear.
What this means for you
If you are handed a positive or negative result and nothing else, you have been given the least useful version of an informative test.
Knowing your figure lets a doctor tell you three things a binary result cannot:
How concerned to be. There is a meaningful difference between 12 and 200, and you deserve to know which one you are.
How quickly to act. Urgency should be proportionate to risk.
What to do if you test again. A figure of 6 last year and 40 this year is information. Two “negatives” would have hidden it entirely.
The one caveat
A low figure is not permission to ignore ongoing symptoms. The Nottingham data shows a 0.1% detection rate below 4, which is low but not zero, and around 1 in 10 cancers occur in people whose FIT sits under the threshold.
Your number tells you where you sit on a scale. It does not tell you to stop paying attention.
References
- Chapman C, et al. Risk stratification by faecal immunochemical test value in a rapid colorectal diagnosis service. BJS Open 2021;5:zraa056.
- National Institute for Health and Care Excellence. Quantitative faecal immunochemical testing to guide colorectal cancer pathway referral in primary care. Diagnostics guidance DG56, 2023.
- 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
Figures are drawn from the sources above. Framing and commentary are the author’s own. Last reviewed August 2026.