Fecal calprotectin test: what does it measure, and when is it useful?

Fecal Calprotectin Test: What It Measures and When It’s Useful

A fecal calprotectin test is a simple, non-invasive stool test that helps your healthcare provider detect inflammation in the gastrointestinal (GI) tract. It’s increasingly used to:

• Screen for inflammatory bowel diseases (IBD) such as Crohn’s disease and ulcerative colitis
• Differentiate IBD from irritable bowel syndrome (IBS)
• Monitor disease activity and response to treatment

Below, we explain what the fecal calprotectin test measures, how it’s performed and interpreted, when it’s most useful, and what to do next.

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What Does the Fecal Calprotectin Test Measure?

Calprotectin is a protein found in white blood cells (neutrophils). When there’s inflammation in the gut lining, neutrophils migrate into the intestinal wall and release calprotectin, which then passes into the stool. Measuring stool calprotectin levels gives an indirect but reliable estimate of gut inflammation.

Key points:

• Calprotectin comes from neutrophils, part of the body’s immune response
• Elevated stool calprotectin = more neutrophils in the gut = more inflammation
• Lower or normal levels suggest little or no inflammation

Because calprotectin is resistant to breakdown in the intestine, it remains stable in stool samples for several days, making the fecal calprotectin test convenient and reliable for outpatient use.

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How the Test Is Performed

1. Sample collection: You collect a small stool sample at home using a special kit provided by your clinic or lab.
2. Sample handling: Seal the sample in the container, label it, and return it to the lab as instructed. No fasting or dietary restrictions are needed.
3. Laboratory analysis: The lab uses an ELISA (enzyme-linked immunosorbent assay) or similar immunoassay to quantify calprotectin concentration, usually reported in micrograms per gram (μg/g).

Results are typically available within a few days.

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Interpreting Fecal Calprotectin Results

Calprotectin Level (μg/g)	Interpretation
< 50	Normal; low probability of IBD
50 – 200	Borderline; may need repeat testing
> 200	High likelihood of active inflammation (e.g., IBD)

• Levels below 50 μg/g make significant gut inflammation very unlikely.
• Borderline results (50–200 μg/g) warrant repeat testing or further evaluation, especially if symptoms persist.
• Very high results (> 200 μg/g) suggest active IBD or another inflammatory condition; your doctor may recommend endoscopy or imaging.

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When the Fecal Calprotectin Test Is Most Useful

1. Differentiating IBD vs. IBS

• IBD (Crohn’s disease, ulcerative colitis) involves GI inflammation
• IBS (irritable bowel syndrome) causes abdominal discomfort without inflammation
• A fecal calprotectin test helps avoid unnecessary colonoscopies in IBS patients by showing low calprotectin levels

2. Initial Assessment of Chronic GI Symptoms

If you have chronic diarrhea, abdominal pain, or unexplained weight loss, a positive fecal calprotectin test points toward an inflammatory cause, prompting timely referral to a gastroenterologist.

3. Monitoring Known IBD

• Track response to medications (biologics, steroids, immunomodulators)
• Detect early relapse before symptoms worsen
• Adjust therapy based on objective inflammation markers rather than symptoms alone

Studies report that monitoring fecal calprotectin can reduce the need for frequent endoscopies and help maintain remission.

4. Evaluating Other Conditions

Less commonly, elevated fecal calprotectin can be seen in:

• Gastrointestinal infections (e.g., bacterial enteritis)
• Colorectal cancer or polyps
• Diverticulitis
• Celiac disease
• Nonsteroidal anti-inflammatory drug (NSAID) enteropathy

Your doctor will interpret the test in the context of your history, exam and other tests.

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Limitations and Considerations

• Not a standalone diagnostic tool: A positive result requires further evaluation (endoscopy, imaging, biopsies).
• Borderline results: May need repeat testing or alternative markers (e.g., lactoferrin).
• False positives: Certain medications (NSAIDs), infections and even intense exercise can transiently raise calprotectin.
• Children vs. adults: Normal ranges may differ slightly; pediatrics often use a cutoff closer to 100 μg/g.

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Next Steps and Talking to Your Doctor

If you’re experiencing persistent GI symptoms—especially chronic diarrhea, blood in stool, abdominal pain or unexplained weight loss—you might consider doing a free, online symptom check for to help clarify your symptoms and decide on the urgency of medical evaluation.

Always discuss your results and concerns with your healthcare provider. If you receive a high fecal calprotectin level or have worrying symptoms, your doctor may recommend:

• Referral to a gastroenterologist
• Colonoscopy with biopsies or advanced imaging
• Blood tests for anemia, inflammation (CRP, ESR) and nutritional deficiencies
• Personalized treatment plans to control inflammation and prevent complications

Speak to a doctor about any severe or life-threatening concerns, including:

• Significant weight loss
• Severe, persistent abdominal pain
• High fever with GI symptoms
• Signs of dehydration

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Bottom Line
The fecal calprotectin test is a practical, non-invasive way to detect and monitor intestinal inflammation. It’s most valuable for distinguishing IBD from IBS, guiding the need for invasive tests, and tracking disease activity in known IBD patients. While it’s not a standalone diagnostic test, it provides critical information that helps your healthcare team make timely, accurate decisions about further evaluation and treatment.