Faecal calprotectin

Also called calprotectin test, stool calprotectin.

Dr Chad OkayFounder, Suna Health

3 min read. Updated .

Faecal calprotectin is a protein released by white blood cells (neutrophils) that lines an inflamed gut. Measuring it in a stool sample distinguishes inflammatory bowel disease (Crohn's, ulcerative colitis) from functional bowel disorders like IBS. On the NHS it is recommended to help tell inflammatory bowel disease apart from IBS when specialist assessment is being considered and cancer is not suspected. Low result reassures; high result triggers a gastroenterology referral.

How it works

When the gut wall is inflamed, neutrophils migrate to the site of inflammation. As they break down, they release calprotectin, which passes into the bowel lumen and shows up in stool. The level correlates well with the degree of gut inflammation visible on colonoscopy. Functional disorders like IBS do not cause inflammation, so calprotectin stays low.

Reading the result

  • Under 50 micrograms/g: normal. Inflammatory bowel disease very unlikely. Reassures functional diagnosis (IBS).
  • 50 to 250 micrograms/g: indeterminate. Could be mild inflammation, recent infection, or NSAID effect. Repeat in 4-6 weeks.
  • Over 250 micrograms/g: significant inflammation. Gastroenterology referral. Possible IBD, infection, polyps or cancer.
  • Lab cutoffs vary slightly; some use 100 instead of 50.

What can falsely elevate it

  • Recent gut infection (gastroenteritis): elevated for 2-4 weeks.
  • NSAIDs (ibuprofen, naproxen, aspirin): can elevate by causing low-grade gut inflammation.
  • PPIs at high doses (smaller effect).
  • Recent endoscopy or colonoscopy.
  • Menstruation contamination of the sample (rare).

When the test earns its place

The test earns its place when a pattern deserves more than watching: a changed bowel habit or diarrhoea that has run past four weeks, blood or mucus, IBS-like patterns alongside a family history of inflammatory bowel disease, a suspected flare of an existing diagnosis, or iron deficiency without an explanation. Your doctor can arrange it, and black or tarry stools are a same-day matter regardless of any pending result.

What the test does NOT diagnose

  • IBS specifically (rules OUT IBD; doesn't confirm IBS).
  • Bile acid diarrhoea (different test, SeHCAT).
  • Coeliac disease (different test, tTG-IgA).
  • Bowel cancer specifically (high values warrant investigation but calprotectin is not a cancer screen).

When not to wait for a test

  • Black, tarry stool or passing a large amount of blood is a same-day emergency: call 999 in the UK or 911 in the US if you also feel faint or are vomiting blood. Do not wait for a calprotectin result.
  • Unintentional weight loss, fever with persistent diarrhoea, or symptoms waking you at night need a doctor promptly, whatever the stool test shows.
  • If symptoms worsen while you are waiting for a result or a repeat test, go back to the doctor rather than waiting out the 4-6 weeks.
  • A normal calprotectin makes inflammatory bowel disease unlikely; it does not rule out everything, so a result that does not fit how unwell you feel deserves a second conversation.

Common questions

Can I get the test on the NHS?
Yes - on the NHS your doctor can order it. NICE recommends faecal calprotectin to help tell inflammatory bowel disease apart from IBS in adults with recent-onset lower bowel symptoms when specialist assessment is being considered and cancer is not suspected. You'll usually be given a stool collection kit to take home.
Should I stop NSAIDs before the test?
Yes, ideally. Ibuprofen, naproxen and aspirin can falsely elevate the result. Stop for 4 weeks if possible, then test.
What if my level is indeterminate?
50-250 is the grey zone. NICE recommends repeating after 4-6 weeks. If still elevated, gastroenterology referral. If a recent gut infection might explain it, waiting is reasonable.
Is it the same as a stool sample for parasites?
No. Faecal calprotectin is a chemical assay. Stool culture/microscopy looks for organisms. Both can be done from the same sample but they're separate tests.

Sources

Written by Dr Chad Okay. Contributor: Dr Parisah Hussain, MBChB, BSc (Hons), DRCOG, MRCGP. Last updated 17 September 2026. From Digests.

Digests explains how the body works in general, everyday terms. It is not medical advice. It is not a substitute for someone who can examine you and knows your history, and we do not tell you what dose of any medicine to take.

Where we describe how something is checked or looked after, we follow UK guidance from NICE and the NHS. If you are reading this outside the UK, the same concerns are worth taking to your own doctor, though the tests and routes where you live may differ.

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