Stool Tests: Fecal Calprotectin

Fecal calprotectin is a stool test that measures a protein released by white blood cells when the gut lining is inflamed. It helps clinicians separate inflammatory bowel disease from non‑inflammatory problems like irritable bowel syndrome and is widely used to track how active Crohn’s disease or ulcerative colitis are between colonoscopies or imaging tests. (en.wikipedia.org)

Key Takeaways

• Fecal calprotectin measures a protein from neutrophils, a type of white blood cell, that appears in stool when the intestinal lining is inflamed. (en.wikipedia.org)

• The test helps distinguish IBD from IBS, because values are usually normal in IBS and raised when the bowel wall is inflamed. (pubmed.ncbi.nlm.nih.gov)

• In people with known IBD, calprotectin tracks gut inflammation over time, often rising before symptoms flare and falling when treatment works. (pubmed.ncbi.nlm.nih.gov)

• Typical “normal” results are below about 50 µg/g, with higher levels suggesting inflammation, although cut‑offs vary by lab and clinical setting. (ncbi.nlm.nih.gov)

• High calprotectin does not always mean IBD, since infections, some medicines, and other bowel diseases can also raise the level. (journals.lww.com)

What fecal calprotectin actually measures

Calprotectin is a small calcium and zinc binding protein found mainly inside neutrophils, which are white blood cells that move into tissues during inflammation. (en.wikipedia.org)

When the lining of the intestine is inflamed, neutrophils move into the gut wall and lumen. As they break down or release their contents, calprotectin is shed into the stool. The more neutrophil activity in the gut, the higher the fecal calprotectin level tends to be. (en.wikipedia.org)

This makes fecal calprotectin a biomarker of neutrophil‑driven intestinal inflammation, rather than a direct test for Crohn’s disease or ulcerative colitis themselves.

Calprotectin is also quite stable in stool for several days at room temperature, which makes it practical for home collection and transport to a lab. (pubmed.ncbi.nlm.nih.gov)

Why fecal calprotectin matters in IBD

Distinguishing IBD from IBS and other non‑inflammatory problems

IBD and irritable bowel syndrome can share symptoms such as diarrhea, abdominal pain, and urgency, but IBS does not involve visible inflammation or tissue damage in the gut.

Studies and guideline reviews show that fecal calprotectin has high sensitivity for detecting bowel inflammation and a strong negative predictive value for ruling out IBD in undiagnosed, symptomatic people. (pubmed.ncbi.nlm.nih.gov)

• At a threshold around 50 µg/g, sensitivity for detecting IBD is often in the 85–95 percent range, with more variable specificity. (ncbi.nlm.nih.gov)

• National bodies such as NICE recommend calprotectin as a tool to help separate suspected IBD from IBS when cancer is not strongly suspected. (nice.org.uk)

If symptoms suggest IBS and the fecal calprotectin is clearly normal, the chance of missing IBD is low, and invasive tests like colonoscopy may be avoided. (ncbi.nlm.nih.gov)

Monitoring known Crohn’s disease and ulcerative colitis

For people already diagnosed with IBD, fecal calprotectin helps track how active intestinal inflammation is between scopes.

Research shows that fecal calprotectin levels:

• Correlate with endoscopic and microscopic inflammation in both Crohn’s disease and ulcerative colitis. (pubmed.ncbi.nlm.nih.gov)

• Tend to fall when treatment induces mucosal healing and rise again before or during relapse. (pubmed.ncbi.nlm.nih.gov)

Modern guidelines from major gastroenterology societies recommend using fecal calprotectin, along with blood markers and symptoms, to guide treat‑to‑target care in both Crohn’s disease and ulcerative colitis. (pubmed.ncbi.nlm.nih.gov)

Because it is noninvasive and repeatable, it is often checked more frequently than colonoscopy, for example:

• To see whether a new therapy is calming inflammation.

• To decide whether a symptom flare might reflect active inflammation or mainly functional symptoms.

• To monitor for “silent” loss of response in someone who feels well. (pmc.ncbi.nlm.nih.gov)

How the test is done

For a standard laboratory test, a stool sample is collected at home into a clean, dry container provided by the lab or clinic. The lab then measures calprotectin concentration, usually reported in micrograms per gram (µg/g) of stool. (understandingibs.org)

There is usually no need for fasting or special diet before collection. The main practical steps involve avoiding contamination with urine or toilet water and following the storage or mailing instructions. (understandingibs.org)

Some services now offer home fecal calprotectin kits that allow testing and result reporting without sending a sample to a central lab. Performance is improving, but accuracy can vary between devices, so results still need clinical interpretation. (pmc.ncbi.nlm.nih.gov)

Understanding typical result ranges

Exact ranges and decision thresholds differ between laboratories and guidelines, but common patterns look like this:

* Units and cut‑offs can change by assay and lab.
** Decisions about endoscopy or treatment are based on the whole clinical picture, not the number alone.

In remission studies, calprotectin levels below about 250 µg/g have shown high sensitivity for endoscopic remission in many IBD cohorts, although some individuals with mild residual inflammation can still fall below that level. (pubmed.ncbi.nlm.nih.gov)

Limits of the test and factors that affect results

Calprotectin is a marker of inflammation in the gut, not a test specific for Crohn’s disease or ulcerative colitis. Other conditions can raise the level, including:

• Intestinal infections.

• Colorectal cancer and some polyps.

• Non‑steroidal anti‑inflammatory drugs (NSAIDs) and some other medications.

• Celiac disease and other inflammatory gut disorders. (journals.lww.com)

Levels can also fluctuate from day to day, especially in milder disease, and cut‑offs for children are often higher than for adults. (pubmed.ncbi.nlm.nih.gov)

A normal fecal calprotectin does not absolutely exclude IBD, particularly if symptoms are severe or persistent, or if inflammation is limited to small bowel segments that are less well reflected in stool markers. (pmc.ncbi.nlm.nih.gov)

Because of these limits, clinicians interpret results together with symptoms, physical exam, blood tests, imaging, and endoscopy findings.

How fecal calprotectin fits into an overall monitoring plan

In IBD care, fecal calprotectin is one part of a treat‑to‑target strategy. The usual goals are:

• Day‑to‑day symptom control.

• Normalization of blood and stool markers of inflammation.

• Healing of the intestinal lining on endoscopy. (pmc.ncbi.nlm.nih.gov)

Fecal calprotectin:

• Helps decide who needs colonoscopy sooner versus later.

• Provides an early signal that inflammation is returning, sometimes before symptoms worsen.

• Can show whether a therapy change is likely helping, even if symptoms improve only slowly. (pubmed.ncbi.nlm.nih.gov)

Regular use of biomarkers, including fecal calprotectin, has been linked with better outcomes in IBD compared with relying on symptoms alone, since silent inflammation can continue even when bowel habits seem acceptable. (news.mayocliniclabs.com)

FAQs

Can someone have IBD with a normal fecal calprotectin?

Yes. A small number of people with IBD, particularly with very mild or limited disease, can have calprotectin values in the normal or borderline range. This is why persistent alarm symptoms still need careful evaluation, even when the stool test is low. (ncbi.nlm.nih.gov)

Does a high calprotectin level always mean a flare?

No. High values signal inflammation but do not explain the cause. In people with known IBD, a rise often reflects a flare, yet infections, medication effects, or other gut diseases can produce a similar increase. Clinical assessment and sometimes endoscopy are needed to clarify the reason. (journals.lww.com)

How often is fecal calprotectin checked in stable IBD?

Guidelines do not set one universal schedule. Many clinicians repeat the test every few months in people with higher relapse risk, after starting or changing therapy, or when symptoms change. The exact timing depends on disease type, severity, treatment, and local practice patterns. (pubmed.ncbi.nlm.nih.gov)

Is fecal calprotectin useful for small bowel Crohn’s disease?

Fecal calprotectin reflects inflammation throughout much of the intestine, including many small bowel areas, but the correlation with activity can be weaker when disease is limited to upper or very proximal small bowel. In that situation, imaging or capsule endoscopy is often needed along with biomarkers. (pmc.ncbi.nlm.nih.gov)