If you live in Glasgow and your neighbour lives in Belfast, the same stool sample could produce a normal result for one of you and a referral for the other. That is not a quirk of the laboratory. It is a policy decision, and it is worth understanding.
The current position
Every UK bowel screening programme uses the same test. What differs is the concentration of haemoglobin treated as positive:
| Nation | Positive at |
|---|---|
| Scotland | 80 µg Hb/g |
| England | 120 µg Hb/g, reducing to 80 in a rollout begun February 2026 |
| Wales | 80 µg Hb/g |
| Northern Ireland | 120 µg Hb/g |
England is reducing its threshold to 80 µg Hb/g in a phased rollout that began in February 2026 and is due to complete by March 2028. Until it completes, which figure applies to you depends on which screening service covers your area.
The symptomatic threshold is not uniform either. NICE sets it at 10 µg Hb/g, which applies in England, Wales and Northern Ireland. Scotland moved to 20 µg Hb/g in its 2025 referral guidance, following updated advice from the Centre for Sustainable Delivery. So a symptomatic sample reading 15 would trigger a referral in Cardiff and would not in Glasgow.
By contrast, when someone has symptoms, the threshold is 10 µg Hb/g everywhere in the UK. That figure does not vary by nation.
Why the difference exists
The honest answer is endoscopy capacity, and there is a piece of evidence that settles it beyond argument.
The UK National Screening Committee has concluded that the optimal threshold is 20 µg Hb/g. It recommended reducing the screening threshold from 120 to 20, and ministers agreed that recommendation. The Committee’s advice is to work towards that figure over time, with careful planning for capacity and feasibility.
So 80 is not the destination. It is as far as the system can currently stretch.
If the concern were that lower thresholds would over-investigate healthy people, the recommended optimum would not be 20, which sits far closer to the symptomatic threshold of 10 than to 80. The constraint is the number of colonoscopies the health service can deliver, not doubt about what the test can detect.
NHS England’s own framing makes the same point. Reducing from 120 to 80 means offering around 35% more screening colonoscopies each year. It is expected to detect roughly 600 more bowel cancers annually in England, an increase of about 11%, find 2,000 more people with high-risk polyps, cut late-stage diagnoses and deaths by around 6%, and save the NHS approximately £32 million a year.
A change that saves both lives and money was phased over years. That tells you what the binding constraint has been.
None of this is a criticism of the programme. Colonoscopy is a good procedure but not a trivial one, it carries a small risk of complications, and there are only so many slots. Allocating them is exactly the job a national screening programme has to do. But it does explain why the number is not the same as the one used when a doctor is assessing one individual with a specific concern.
Why it matters for you
Two practical consequences.
Your screening result is relative to where you live. A figure of 100 is normal in England today, would be positive in Scotland, and would remain normal in Wales. Same sample, same test, different letter.
A normal screening result is not the same as being cleared. This is the point that matters most. Applied to people with symptoms, high thresholds miss a great deal: pooled data from symptomatic patients found that thresholds of 100 and 150 detected 68.1% and 66.3% of colorectal cancers, against 88.7% at 10.
This is exactly why NICE states that FIT should be offered to someone with symptoms even if they have already had a negative result through the NHS screening programme.
What to do with this
If you are within the screening age range, take the free test when it arrives. It is doing the job it was designed for, and the programme saves lives.
But treat the result as what it is: an answer to the question “was there a substantial amount of blood in this sample?” That is a useful question. It is not the same as “is everything fine?”
If you develop symptoms afterwards, the screening letter should not stop you acting on them.
References
- NHS England. Announcement on reducing the bowel cancer screening FIT threshold, January 2026; and The National Cancer Plan for England, 2026.
- 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.
- Scottish Government. FIT testing for patients with colorectal symptoms: primary care guidance, 2022.
- UK National Screening Committee. Recommendation on the FIT screening threshold, and More sensitive bowel cancer screening test implemented in line with UK NSC recommendation, national screening blog, January 2026.
- NHS England. NHS to detect and prevent thousands more bowel cancers with more sensitive screening, January 2026.
Figures are drawn from the sources above. Framing and commentary are the author’s own. Last reviewed August 2026.