What it measures.
Fecal calprotectin is a protein released by neutrophils in the intestinal lining during inflammation. It is the most validated non-invasive marker for distinguishing inflammatory bowel disease (IBD) from irritable bowel syndrome (IBS), with sensitivity >90% and negative predictive value >95%. A normal result effectively rules out significant intestinal inflammation without endoscopy.
Calprotectin concentration in a stool sample, reflecting neutrophilic inflammation in the intestinal mucosa. It is proportional to the number of neutrophils migrating into the gut lumen — a direct measure of mucosal inflammation. Note: this is a stool test, not a blood test.
Why it matters.
Calprotectin transforms the chronic diarrhoea workup. Instead of every patient with persistent GI symptoms requiring colonoscopy, calprotectin triages effectively: normal values rule out IBD with >95% confidence, while elevated values identify patients who need endoscopy. In known IBD, serial calprotectin monitoring predicts relapse 2-3 months before symptoms worsen.
Physiology.
Calprotectin is a calcium- and zinc-binding protein constituting ~60% of neutrophil cytoplasmic protein. When neutrophils migrate into the gut wall during inflammation, calprotectin is released into the intestinal lumen and excreted in stool. It is stable in stool at room temperature for up to 7 days, making it practical for outpatient collection.
Testing & preparation.
How to prepare
- Stool sample (not blood) — collected at home in a provided container
- No fasting required
- Avoid NSAIDs for 2 weeks before testing (NSAIDs elevate calprotectin)
- PPIs do not significantly affect results
- Sample stable at room temperature for up to 7 days
When to test
Chronic diarrhoea >4 weeks to differentiate IBD from IBS. Monitoring known IBD treatment response. Predicting IBD relapse in remission. Chronic abdominal symptoms with concern for organic pathology.
How often
In known IBD: every 3-6 months during remission. After medication changes: recheck in 8-12 weeks.
Interpretation.
High fecal calprotectin
Common causes:
- Inflammatory bowel disease (Crohn's, UC) — most common clinically significant cause
- Intestinal infections (bacterial, parasitic)
- NSAID-induced enteropathy
- Colorectal cancer (but not a screening tool for cancer)
- Microscopic colitis
- Diverticulitis (during acute episode)
Implications:
- <50 μg/g: IBD very unlikely — supports IBS or functional diagnosis
- 50-250 μg/g: indeterminate — repeat in 4-6 weeks; consider endoscopy if clinically suspicious
- >250 μg/g: strongly suggests intestinal inflammation — endoscopy referral recommended
- >500 μg/g: active IBD very likely; correlates with endoscopic disease severity
Low fecal calprotectin
Common causes:
- Normal intestinal mucosa (no inflammation)
- Functional GI disorders (IBS, functional dyspepsia)
- No clinically significant cause of low calprotectin
Implications:
- Normal calprotectin is one of the most useful 'rule-out' results in GI medicine
- Effectively excludes IBD with >95% negative predictive value
- Supports functional diagnosis without need for invasive endoscopy
Optimization.
Diet
- Anti-inflammatory diet patterns may reduce calprotectin in mild cases
- Mediterranean diet associated with lower calprotectin in IBD remission
- Exclusive enteral nutrition reduces calprotectin in Crohn's disease (paediatric evidence strongest)
Lifestyle
- Regular exercise associated with lower intestinal inflammation markers
- Stress management — the gut-brain axis modulates intestinal inflammation
- Smoking cessation — smoking worsens Crohn's disease inflammation
Supplements
- No supplements reliably lower calprotectin in active IBD
- Probiotics: modest evidence in UC maintenance remission; limited evidence in Crohn's
FAQs.
Is fecal calprotectin a blood test?
No — it's a stool test. You collect a stool sample at home in a provided container and return it to the lab. It's non-invasive, stable at room temperature for up to 7 days, and doesn't require fasting.
If my calprotectin is normal, do I still need a colonoscopy?
In most cases, no. A normal calprotectin (<50 μg/g) effectively rules out IBD with >95% negative predictive value. However, colonoscopy is still needed for age-appropriate cancer screening (45+), alarm symptoms (rectal bleeding, weight loss), or family history of colorectal cancer regardless of calprotectin.
Can IBS cause elevated calprotectin?
IBS does not cause significant calprotectin elevation. Values <50 μg/g are typical in IBS. If calprotectin is elevated (>250 μg/g) in someone labelled with IBS, the diagnosis should be reconsidered and endoscopy performed to rule out IBD or other organic pathology.