IBS and IBD

Faecal calprotectin

Also called: calprotectin test, stool calprotectin

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 to ask for the test

  • Ongoing diarrhoea or change in bowel habit lasting over 4 weeks.
  • Blood or mucus in stool.
  • IBS-like symptoms in someone with family history of IBD.
  • Suspected IBD relapse on existing diagnosis.
  • Iron deficiency anaemia not explained by diet or periods.

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).

Common questions

Can I get the test on the NHS?
Yes, GPs 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

The Book of Suna is general information, not medical advice. It is not a substitute for talking to a qualified healthcare professional about your own situation.