A fecal calprotectin test measures a neutrophil-derived protein in stool. When the intestinal lining is inflamed, neutrophils move into the gut and release calprotectin, causing the stool concentration to rise. The test is widely used to help distinguish inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis, from noninflammatory conditions such as irritable bowel syndrome. It can also monitor known IBD, assess treatment response, and help decide when endoscopy may be needed. A high result does not diagnose IBD by itself. Gastrointestinal infection, nonsteroidal anti-inflammatory drugs, bleeding, polyps, cancer, and other bowel disorders may also raise it. Cutoffs vary by assay, age, and clinical pathway, and borderline results are often repeated. This article explains common ranges, sample collection, causes of high levels, IBD monitoring, medication effects, and how clinicians combine fecal calprotectin with symptoms and other tests.
- Gut-focused marker: Fecal calprotectin reflects neutrophil activity in the intestinal tract more directly than blood markers.
- Useful for IBD versus IBS: A low result makes active inflammatory bowel disease less likely in many symptomatic adults.
- Cutoffs differ: Less than 50 µg/g is commonly considered normal, but laboratories and pathways use different thresholds.
- High is not specific: Infection, NSAIDs, bleeding, neoplasia, and other inflammation can raise the value.
- Trends guide monitoring: In established IBD, repeated results can help assess mucosal inflammation and relapse risk.
Table of Contents
- How Fecal Calprotectin Reflects Gut Inflammation
- Normal, Borderline, and High Ranges
- IBD Versus IBS and Diagnostic Use
- Causes of High Fecal Calprotectin
- Monitoring Crohn’s Disease and Ulcerative Colitis
- Collection, Medications, and Test Limitations
- Follow-Up After an Abnormal Result
How Fecal Calprotectin Reflects Gut Inflammation
Calprotectin is a complex of the S100A8 and S100A9 proteins. It is abundant in neutrophils, which are white blood cells that respond rapidly to infection and tissue injury. When the intestinal mucosa becomes inflamed, neutrophils migrate from blood vessels through the bowel wall and into the intestinal lumen. Calprotectin released from these cells mixes with stool.
The protein is relatively stable in feces, making it practical for noninvasive testing. The laboratory extracts calprotectin from a small stool sample and reports the concentration, usually in micrograms per gram of stool, written µg/g or mcg/g.
Fecal calprotectin is not the same as circulating calprotectin. The calprotectin blood test reflects systemic neutrophil and monocyte activation and uses serum or plasma. The stool test is more focused on inflammation within the gastrointestinal tract.
A high stool concentration tells clinicians that neutrophils are entering the bowel, but it does not identify the cause or exact location. Colon inflammation often produces a strong signal because calprotectin mixes directly with stool. Disease limited to a short segment of the small intestine may produce a lower or more variable result. Patchy disease, sample variation, and treatment can also affect the number.
The test is valuable because symptoms alone can be misleading. Abdominal pain, bloating, diarrhea, and altered bowel habits occur in both inflammatory bowel disease and irritable bowel syndrome. IBS changes bowel function without causing the neutrophil-rich mucosal inflammation typical of active IBD. A low fecal calprotectin can therefore reduce the likelihood that active IBD is driving symptoms, while a high value supports further investigation.
The marker is not a substitute for endoscopy, biopsy, or imaging when those tests are clinically indicated. It is a triage and monitoring tool that can reduce unnecessary invasive procedures in carefully selected patients.
Normal, Borderline, and High Ranges
Many laboratories use less than 50 µg/g as a normal adult result. One major reference laboratory categorizes 50–120 µg/g as borderline and above 120 µg/g as abnormal. Other clinical pathways use wider bands, such as below 100, 100–250, and above 250 µg/g. These differences reflect assay performance, intended use, age group, and local referral policy.
| Illustrative result | Common interpretation | Typical next consideration |
|---|---|---|
| Below 50 µg/g | Low likelihood of substantial neutrophilic intestinal inflammation | Consider functional or other noninflammatory causes if symptoms persist |
| 50–120 or 50–150 µg/g | Borderline or mildly elevated | Review medications, recent infection, age, and repeat testing when appropriate |
| About 150–250 µg/g | Increasing likelihood of organic intestinal inflammation | Clinical review and possible gastroenterology investigation |
| Above 250 µg/g | Active inflammation becomes more likely | Prompt evaluation, especially with red flags or known IBD |
| Very high, such as above 500–600 µg/g | Marked intestinal neutrophil activity | IBD flare or infection may be likely, but the cause still requires confirmation |
These are not universal diagnostic thresholds. A result of 70 µg/g may be labeled borderline by one laboratory and low-risk by another pathway. A result of 200 µg/g can have different meaning in a healthy young adult with new diarrhea, an older adult with bleeding, and a person with established ulcerative colitis.
Age matters. Infants and young children can have higher baseline concentrations, and pediatric cutoffs require age-appropriate interpretation. Older adults have a higher probability of non-IBD organic disease, including neoplasia, so fecal calprotectin should not be used to delay indicated cancer evaluation.
The test has no single “critical value” equivalent to an immediately dangerous electrolyte result. Urgency depends on symptoms. A person with severe bloody diarrhea, dehydration, fever, weight loss, anemia, or abdominal tenderness may need rapid assessment even before the result returns.
IBD Versus IBS and Diagnostic Use
The best-established diagnostic use is helping distinguish IBD from IBS in patients with persistent lower gastrointestinal symptoms when cancer is not suspected. NICE guidance supports fecal calprotectin as an option in this setting because IBD involves intestinal inflammation while IBS does not.
A low result has strong negative predictive value in many adult primary-care populations. That means active IBD becomes less likely when the test is low, particularly if there are no red flags and the pretest probability was modest. It does not mean IBD is impossible.
False-negative or unexpectedly low results can occur with:
- Early or mild disease
- Inflammation limited mainly to the small bowel
- Patchy Crohn’s disease
- Recent effective treatment
- Sampling variation
- Some pediatric presentations
A high result increases the likelihood of organic inflammation but does not distinguish Crohn’s disease from ulcerative colitis, infection, drug injury, diverticulitis, or cancer. Endoscopy with biopsy remains central for diagnosing and classifying IBD. Small-bowel imaging may be needed when Crohn’s disease is suspected beyond the reach of standard colonoscopy.
The test should not be used as a gatekeeper when alarm features are present. Rectal bleeding, iron-deficiency anemia, an abdominal mass, persistent vomiting, unexplained weight loss, a strong family history of colorectal cancer, or symptoms beginning at an older age may justify direct referral or endoscopy regardless of calprotectin.
Stool pathogen testing may be needed when diarrhea is acute, follows travel or antibiotics, occurs during an outbreak, or is accompanied by fever. Infection can produce a very high calprotectin and may temporarily mimic an IBD flare.
Causes of High Fecal Calprotectin
Fecal calprotectin rises whenever neutrophils enter the intestinal lumen. IBD is a major cause, but the differential is broader.
Crohn’s disease and ulcerative colitis often produce sustained elevations during active mucosal inflammation. Values may correlate with endoscopic activity, particularly in colonic disease.
Infectious gastroenteritis can cause large increases. Bacterial infections often produce strong neutrophil responses, but viral and parasitic infections may also elevate the marker. The value may fall after the infection resolves.
Nonsteroidal anti-inflammatory drugs, including ibuprofen, naproxen, and aspirin, can injure the gastrointestinal lining and raise calprotectin. The effect varies by dose, duration, and individual susceptibility.
Proton pump inhibitors have been associated with modest elevations in some studies. They should not be stopped without medical advice, especially when used for ulcer prevention or significant acid-related disease.
Diverticulitis and other inflammatory conditions of the colon may increase the test. Microscopic colitis can also produce variable elevations, though a normal value does not reliably exclude it.
Gastrointestinal bleeding may affect the result, particularly when bleeding reflects an inflammatory or structural lesion. Calprotectin is not a test for locating bleeding.
Polyps and colorectal cancer can raise fecal calprotectin, but the test is neither sensitive nor specific enough for cancer screening. Standard screening and urgent referral pathways should be followed.
Celiac disease may produce mild elevation in some patients, especially with active inflammation, but fecal calprotectin is not the primary diagnostic test. Tissue transglutaminase antibodies and confirmatory evaluation are more appropriate.
Recent gastrointestinal surgery, radiation injury, or other mucosal damage may also increase the concentration.
Because so many causes overlap, “high calprotectin equals IBD” is an unsafe shortcut. The duration and character of symptoms, age, medication history, stool cultures, blood tests, and endoscopic findings determine the diagnosis.
Monitoring Crohn’s Disease and Ulcerative Colitis
In established IBD, symptoms do not always match mucosal inflammation. A patient may feel well while inflammation continues, or may have pain and diarrhea from IBS, bile-acid malabsorption, infection, or scarring despite controlled inflammation. Fecal calprotectin helps separate these possibilities.
The American Gastroenterological Association recommends using noninvasive biomarkers, including fecal calprotectin, to inform monitoring in ulcerative colitis. Modern Crohn’s disease guidance also supports its use when the disease location is known to produce a reliable baseline signal.
A low value during symptomatic remission can support continued monitoring rather than routine immediate endoscopy in selected patients. An elevated value may prompt repeat testing, treatment review, imaging, or endoscopic assessment. The exact action depends on the treatment target and the patient’s history.
Trends are especially useful. A fall from 1,200 to 250 µg/g may indicate major improvement even though inflammation may remain. A rise from 80 to 400 µg/g in a previously stable patient may suggest relapse before symptoms become severe. Small changes can reflect day-to-day and within-stool variation.
Calprotectin tends to correlate better with colonic inflammation than isolated ileal Crohn’s disease. A person with known small-bowel disease may need imaging or other markers even when the stool result is modest. Strictures and fistulas can cause symptoms that are not fully represented by the calprotectin concentration.
Treatment should not be changed solely from one unexpected result. Before escalating immunosuppression, clinicians may exclude infection, review medication adherence, repeat the sample, and assess other evidence. The CRP blood test, blood count, albumin, symptoms, and imaging may provide complementary information.
Repeated biomarker monitoring can reduce the need for some colonoscopies, but it cannot replace endoscopic surveillance for dysplasia or cancer in people with longstanding colitis. Disease control and cancer prevention are separate clinical goals.
Collection, Medications, and Test Limitations
The test usually begins with a home collection kit. Instructions vary, so use the device supplied by the laboratory. In general, stool should be passed into a clean, dry collection surface rather than directly into toilet water. A small sample is transferred into the container without contamination by urine, cleaning products, or menstrual blood.
The sample may be taken from more than one area of the stool because calprotectin is not always evenly distributed. The container should be closed securely, labeled, and returned according to temperature and timing instructions. Some samples are stable for several days when refrigerated, but the laboratory’s directions take priority.
No dietary preparation or fasting is usually required. Medication decisions are more complicated. NSAIDs and possibly proton pump inhibitors can elevate the result. A clinician may advise a temporary pause before repeat testing when it is safe, but patients should not stop prescribed aspirin, anticoagulation-related therapy, or ulcer-protective medication on their own.
Limitations include:
- Variation within a bowel movement and from day to day
- Differences among assays and extraction devices
- Higher normal values in infancy
- Reduced sensitivity for isolated small-bowel disease
- False elevation from infection or medication-related injury
- Inability to identify the exact disease or location
Repeating a borderline result can reduce random error. Many pathways suggest retesting after several weeks once infection has resolved and potentially interfering medication has been reviewed. A clearly high value with alarm symptoms should not be delayed merely to obtain a second sample.
Blood contamination can complicate interpretation, but visible blood is itself a reason for clinical assessment. The test should not be used to reassure someone with persistent rectal bleeding when investigation is otherwise indicated.
Follow-Up After an Abnormal Result
The next step depends on whether the test was ordered for new symptoms or for known IBD.
For new symptoms, clinicians may:
- Review the value against the laboratory’s cutoff and the patient’s age.
- Check for red flags, recent infection, travel, antibiotics, NSAID use, and family history.
- Order blood counts, CRP, celiac testing, stool cultures, or other targeted studies.
- Repeat a borderline result after temporary causes are addressed.
- Refer for colonoscopy, imaging, or specialist assessment when inflammation remains likely.
For known IBD, follow-up may include confirming medication adherence, checking for infection, comparing prior calprotectin values, and deciding whether treatment adjustment or endoscopic assessment is needed. A single high value in an otherwise stable patient may be repeated, while a high value with bleeding, nocturnal diarrhea, weight loss, or rising CRP may require faster action.
Seek urgent care for severe abdominal pain with guarding, repeated bloody stools, fainting, inability to keep fluids down, signs of dehydration, high fever, marked weakness, or a swollen abdomen with inability to pass stool or gas. These symptoms may indicate severe colitis, obstruction, infection, or another urgent condition. The seriousness comes from the clinical picture, not the calprotectin number alone.
A low result is reassuring only within the question the test can answer. It supports a low likelihood of substantial neutrophilic gut inflammation, but it does not diagnose IBS, exclude every bowel disorder, or remove the need for age-appropriate cancer screening.
Used correctly, fecal calprotectin is a practical bridge between symptoms and invasive testing. It is most valuable when the result changes a defined decision: whether to investigate for IBD, whether inflammation is controlled, or whether a flare needs confirmation.
Why Repeat Results Can Differ
Fecal calprotectin is released into stool unevenly, so two samples from the same person can differ even when symptoms have not changed much. Day-to-day variation may reflect where inflammation is occurring, how active it is, recent medicines, an infection, or ordinary differences between bowel movements. A single value near a decision threshold should therefore be interpreted cautiously. When the result is borderline and there are no urgent warning signs, clinicians often repeat the test after a suitable interval and review possible temporary causes rather than making a diagnosis from one number.
For follow-up, trends are most useful when samples are tested by the same laboratory method. Different assays can use different antibodies, extraction systems, and cutoffs, so a change after switching laboratories may not represent a true biological change. A falling result can support improving intestinal inflammation, while a persistently high or rising result may prompt closer assessment even when symptoms seem mild. However, symptom relief and mucosal healing are not identical: some people feel better while inflammation remains, and others have symptoms from scarring, bile acid problems, or irritable bowel features despite a low result.
Children, older adults, and people with recent gastrointestinal bleeding may need age- and context-specific interpretation. Fecal calprotectin also does not replace colorectal cancer screening or investigation of anemia, weight loss, rectal bleeding, or other alarm features.
References
– Calprotectin Stool Test 2024 – CALPR – Overview: Calprotectin, Feces 2026 – AGA Clinical Practice Guideline on the Role of Biomarkers for the Management of Ulcerative Colitis 2023 – Biomarkers in Inflammatory Bowel Disease: A Practical Guide 2024 – British Society of Gastroenterology Guidelines on Inflammatory Bowel Disease in Adults: 2025 2025 – Faecal Calprotectin Diagnostic Tests for Inflammatory Diseases of the Bowel 2013
Disclaimer
This article is for general education and cannot diagnose or exclude IBD from a fecal calprotectin result. Cutoffs vary by laboratory, age, assay, medication exposure, and clinical pathway, and infection or other bowel disease can raise the value. Persistent symptoms, alarm features, or abnormal trends should be assessed by a qualified healthcare professional.
