Faecal Calprotectin Interpreter
Faecal Calprotectin Interpreter
Read a faecal calprotectin against the threshold that matches the question being asked, and against the drugs and conditions that raise it.
Faecal calprotectin
Result + context → interpretationFaecal calprotectin 180 µg/g in a patient with new lower gastrointestinal symptoms who has been taking ibuprofen
Two thresholds, two questions
Assessing mucosal healing in known IBD: 250 µg/g
- 50 µg/g
- the cut-off NICE DG11 and the NIHR review use for ELISA methods in symptomatic patients; optimal for detecting endoscopic activity (sensitivity 0.88, specificity 0.73)
- 15 µg/g
- the cut-off for the PreventID point-of-care test — the same analyte, a different assay, a different number
- 100 µg/g
- the lower operational boundary in most NHS primary care pathways; below it the probability of IBD is under 2%
- 250 µg/g
- urgent-referral threshold in primary care (about 46% probability of IBD), and separately the mucosal-healing threshold in known IBD
- 200 µg/g
- a paediatric cut-off recorded in use by some laboratories in the NIHR review
Worked example
Faecal calprotectin 180 µg/g in a patient with new lower gastrointestinal symptoms who has been taking ibuprofen
180 µg/g is above 100 and below 250 → the intermediate band, about a 12% probability of inflammatory bowel disease
NSAIDs raise faecal calprotectin independently of IBD
→ stop the NSAID and repeat before referring; the drug is the more likely of the two explanations
Bands in the diagnostic setting
| Calprotectin | Probability of IBD | Action |
|---|---|---|
| < 100 µg/g | under 2% | Treat as functional; no colonoscopy on this basis |
| 100–250 µg/g | about 12% | Withhold NSAIDs and PPIs, repeat in 4–6 weeks, exclude infection |
| > 250 µg/g | about 46% | Urgent referral to gastroenterology |
Raised calprotectin that is not IBD
| Cause | Why it matters |
|---|---|
| NSAIDs | Very common, often not volunteered, and enough on its own to push a result into the intermediate band. Withhold and repeat. |
| Proton pump inhibitors | An independent association. NHS pathways advise stopping for two to six weeks before a repeat where clinically possible. |
| Age | NICE DG11 restricts the test to patients in whom cancer is not suspected, naming age as a risk factor. In adults aged 50 and over the positive predictive value at 50 µg/g was 12.8% (95% CI 7.9 to 20.1) — about one raised result in eight was IBD. |
| Gastrointestinal infection | Including Clostridioides difficile and Giardia. Calprotectin should normalise afterwards, which is the argument for repeating rather than referring. |
| Neoplasia | Colorectal cancer and adenomas of 10 mm or more both raise it. A high result is a reason to investigate, not a reason to assume IBD. |
| Coeliac disease, diverticulitis, cirrhosis | All listed as causes of a raised result by NHS laboratory guidance. |
One analyte, several thresholds, and why that is not sloppiness
Faecal calprotectin became a routine test in the UK because of NICE DG11, which recommended it "as an option to support clinicians with the differential diagnosis of inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS) in adults with recent onset lower gastrointestinal symptoms for whom specialist assessment is being considered" — with two conditions attached, that cancer is not suspected having considered risk factors including age, and that quality assurance and local pathways are in place. Both conditions are load-bearing and both are routinely dropped when the test is quoted.
The thresholds are assay- and laboratory-specific, and that is a property of the measurement rather than a caveat added for safety. The NIHR review underpinning DG11 assessed twelve different calprotectin tests. It recommended 50 µg/g for ELISA methods, recorded 15 µg/g for the PreventID point-of-care test, and noted a 200 µg/g paediatric cut-off in use in some practices. Different antibodies, different extraction protocols, different calibration. A result of 80 µg/g means something different depending on which platform produced it, and the only threshold that applies to your patient is the one on your own laboratory's report.
The two figures most often quoted — 50 and 250 µg/g — are not competing estimates of the same boundary. They answer different questions, and Mosli's meta-analysis says so in as many words: the 50 µg/g cut-off "that was identified as optimal for the detection of endoscopically active disease in symptomatic patients is substantially different from the value of 250 µg/g reported by Lin et al. in patients whose disease was in symptomatic remission". Fifty is a rule-out threshold for a patient who has not yet been diagnosed. Two hundred and fifty is a mucosal-healing threshold for a patient who has. Using the first on a patient in remission generates alarm; using the second on a new presentation misses disease. The context selector above exists for that reason.
Even at its best the test is a probability, not an answer. At 50 µg/g in symptomatic patients, pooled sensitivity against endoscopic activity is 0.88 and specificity 0.73 — 0.79 in ulcerative colitis, 0.67 in Crohn's disease. In practice that means the negative result is worth much more than the positive one, which is exactly how NHS pathways use it: below 100 µg/g the probability of inflammatory bowel disease is under 2% and a colonoscopy is hard to justify; above 250 µg/g it is about 46% and a referral is; in between it is about 12% and the right move is usually to repeat the test with the confounders removed.
Those confounders are ordinary. NSAIDs and proton pump inhibitors both raise calprotectin independently of inflammatory bowel disease, and both are common enough that a single intermediate result in a young patient with typical irritable bowel symptoms is more likely to be explained by ibuprofen than by Crohn's disease. That is an argument from pre-test probability rather than a figure anyone has published head-to-head: Crohn's disease is uncommon, NSAID use is not, and the same 180 µg/g is consistent with both. Infection, Clostridioides difficile, coeliac disease, diverticulitis, cirrhosis and colorectal neoplasia all do the same thing. In adults aged 50 and over the positive predictive value at the 50 µg/g cut-off was 12.8%, with polyps of 10 mm or more and diverticular disease the commonest alternative findings — which is why the authors of that study proposed the test as a rule-out in that age group rather than as a way in to endoscopy.
Finally, the number is not linear with disease activity. In a pooled analysis of ulcerative colitis, median calprotectin by Mayo endoscopic subscore ran 94, 168, 428 and 780 µg/g for subscores 0 to 3 — an ordering, not a scale. A calprotectin of 900 µg/g does not indicate twice the inflammation of 450, and a fall from 900 to 450 on treatment is not half a response. Trend it, band it, and let endoscopy grade it.
Frequently asked questions
What is a normal faecal calprotectin?
It depends on the assay. NICE DG11's underpinning review recommends 50 µg/g for ELISA methods, 15 µg/g for the PreventID point-of-care test, and records a 200 µg/g paediatric cut-off in use in some laboratories. Most NHS primary care pathways operate on 100 and 250 µg/g rather than 50. Use the threshold printed on your own laboratory's report.
Why do 50 µg/g and 250 µg/g both get quoted?
Because they answer different questions. 50 µg/g is the cut-off optimal for detecting endoscopic activity in symptomatic patients who have not been diagnosed. 250 µg/g is the value used to assess mucosal healing in patients with known inflammatory bowel disease in symptomatic remission. Mosli's meta-analysis makes that distinction explicitly.
Can NSAIDs cause a raised faecal calprotectin?
Yes, and so can proton pump inhibitors, independently of any inflammatory bowel disease. NHS pathways advise withholding them and repeating: two weeks off a PPI in one guideline, four to six weeks off both in another. In an intermediate result in a young patient with typical irritable bowel symptoms, the drug is usually the more likely explanation.
Does a higher calprotectin mean worse disease?
Not proportionally. Median values by Mayo endoscopic subscore in ulcerative colitis were 94, 168, 428 and 780 µg/g for subscores 0 to 3 — the ordering holds but the scale does not. A result of 900 does not mean twice the inflammation of 450.
Does a normal calprotectin exclude bowel cancer?
No. NICE DG11 recommends the test only where cancer is not suspected, having considered risk factors including age, and colorectal neoplasia can present with a result below the cut-off. In adults aged 50 and over, polyps of 10 mm or more were among the commonest findings behind a raised result. A calprotectin is not a substitute for a cancer pathway.
Related calculators
References
- National Institute for Health and Care Excellence. Faecal calprotectin diagnostic tests for inflammatory diseases of the bowel. NICE diagnostics guidance DG11. 2013.
- Waugh N, Cummins E, Royle P, et al. Faecal calprotectin testing for differentiating amongst inflammatory and non-inflammatory bowel diseases: systematic review and economic evaluation. Health Technol Assess. NIHR; NCBI Bookshelf NBK261316.
- Mosli MH, Zou G, Garg SK, et al. C-reactive protein, fecal calprotectin, and stool lactoferrin for detection of endoscopic activity in symptomatic inflammatory bowel disease patients: a systematic review and meta-analysis. Am J Gastroenterol. 2015;110(6):802–19.
- Perry RW, Foulser PFG, Zhang D, et al. Evaluating the role of faecal calprotectin in older adults: a retrospective observational study. Br J Gen Pract. 2025. doi:10.3399/BJGP.2025.0169.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.