Calprotectin Test · Stool

If you have had months of cramping, urgency, or loose stools and your blood work keeps coming back normal, this is the test that answers the question your doctor probably keeps asking: is this inflammation in the bowel, or is this a functional gut issue? Calprotectin is a protein released by white blood cells when they flood into the lining of your intestines, and measuring it in stool gives you a direct read on whether that attack is happening right now.

A normal result can rule out inflammatory bowel disease with high confidence in most adults, often sparing you a colonoscopy. A high result redirects the workup toward a real inflammatory diagnosis instead of years spent managing the wrong condition. For people already living with Crohn's disease or ulcerative colitis, it is the most useful home-friendly way to track whether a quiet-looking remission is about to flare.

What This Test Actually Measures

Calprotectin (the protein complex known to scientists as S100A8/S100A9) is stored in large amounts inside neutrophils, the first-responder white blood cells of your immune system. When your gut lining is inflamed, neutrophils migrate into the intestinal wall and eventually into the stool itself, releasing calprotectin along the way. The stool test captures that released protein as a direct measure of how much neutrophil activity is happening in your intestines.

Because the protein is very stable in stool and rises roughly in proportion to the number of neutrophils in the bowel, it acts as a quantitative marker of intestinal inflammation specifically. Unlike a blood inflammation marker such as CRP (C-reactive protein, a general signal of inflammation anywhere in the body), stool calprotectin does not usually move in response to a cold, a joint flare, or a viral illness. It is tissue-specific in a way most inflammation markers are not.

Telling IBD Apart from Irritable Bowel

The biggest practical value of this test is separating inflammatory bowel disease (IBD), which describes Crohn's disease and ulcerative colitis, from irritable bowel syndrome (IBS), a condition where the gut behaves abnormally without inflammation. The symptoms overlap almost completely, but the treatments, prognosis, and long-term consequences are very different.

In adults with suspected IBD, a large meta-analysis found that calprotectin testing correctly flagged active disease about 93 out of 100 times and correctly cleared healthy bowels about 96 out of 100 times at a cutoff around 50 micrograms per gram. Using the test as a triage step can cut the number of unnecessary colonoscopies by roughly 67%. In children and teens, sensitivity is similarly high but specificity drops, meaning more false positives and more follow-up imaging needed to confirm.

What this means for you: if you have chronic gut symptoms and no red-flag findings (no weight loss, no blood, no anemia), a low calprotectin is one of the strongest ways to avoid going straight to a colonoscopy. A clearly elevated number, especially above 250 micrograms per gram, is a signal to move the investigation forward rather than wait.

Predicting Flares in Known IBD

Once IBD is diagnosed, calprotectin becomes a surveillance tool. The protein often rises weeks to months before a flare causes symptoms, giving you a window to adjust therapy while the inflammation is still mild. In patients in clinical remission, repeatedly elevated readings predict relapse within two to three months, with about a 53 to 83 percent chance of flare if two consecutive tests are high, and a 67 to 94 percent chance of staying well if they remain normal.

In ulcerative colitis patients treated with biologics, those whose post-induction calprotectin dropped below 250 micrograms per gram had substantially higher rates of long-term clinical, endoscopic, and histological remission, along with lower rates of colectomy and hospitalization. This is why modern IBD care treats calprotectin as a target, not just a number.

Small-Bowel Crohn's Disease

Colonoscopy only sees the large intestine and the very end of the small intestine. Inflammation further up the small bowel can be invisible to a standard scope. For suspected small-bowel Crohn's disease, calprotectin at a cutoff around 100 micrograms per gram is a reasonable screen to decide whether to go on to capsule endoscopy. This is one of the few non-invasive ways to catch inflammation in a part of the gut that is otherwise hard to reach.

Other Causes of Elevated Calprotectin

Calprotectin is sensitive, not specific. It tells you that neutrophils are in your gut lining, but not why. Elevations can also come from acute gastroenteritis, diverticular disease, colorectal polyps or cancer, drug-induced enteropathy (bowel injury caused by medication), and in older adults, age and obesity. This is why a single elevated number is a starting point, not a diagnosis.

Reference Ranges

These thresholds are drawn from the largest clinical studies of symptomatic adults. They are widely used but not universally standardized, and different assays can give different numbers for the same sample. Your lab will likely report a specific cutoff; compare your results within the same lab and same test kit over time for the most meaningful trend.

Note that cutoffs are higher in young children, where the normal intestinal barrier is still developing, and position papers emphasize not applying adult cutoffs to infants and toddlers. For people with known IBD, a post-treatment value below 250 micrograms per gram has been tied to better long-term remission and fewer hospitalizations.

Tracking Your Trend

A single calprotectin result can swing widely. Within a single stool sample, the variability is modest (around 17%), but between two stools collected one to six days apart, the variability jumps to around 36%. In people with active ulcerative colitis, same-day variability can reach a median of 52%. Bowel movements after a longer gap tend to read higher than those after a shorter gap.

This is why trend matters more than any one reading. For a first test, sample from the first bowel movement of the morning. If you are investigating symptoms, retest in 4 to 6 weeks before making a decision. If you are living with IBD, every 3 to 6 months while stable, and more often if starting or changing therapy, gives you the early warning the test is designed to provide.

When Results Can Be Misleading

• NSAIDs: Over-the-counter painkillers like ibuprofen and naproxen injure the intestinal lining in a way that releases calprotectin. A mild elevation while taking them does not mean you have IBD. Stop NSAIDs for at least two weeks before testing.
• Proton pump inhibitors: Medications like omeprazole, pantoprazole, and esomeprazole can raise stool calprotectin, likely through changes in gut bacteria. They do not cause IBD, but can push a borderline number into the grey zone.
• Recent gastroenteritis: A bout of food poisoning or a viral stomach bug can keep calprotectin elevated for weeks after symptoms resolve. Wait at least a month after a gut infection before drawing conclusions from a high result.
• Sample handling: Calprotectin is stable at room temperature for about 3 days, but drops by roughly 28% by day 7. Ship the sample quickly and keep it refrigerated between collection and shipment.

What to Do with an Abnormal Result

If your result is above 250 micrograms per gram, the next step is not another stool test. It is a referral to a gastroenterologist for direct visualization of the intestine, usually a colonoscopy with biopsies. If your result sits in the grey zone between 50 and 250 and you have ongoing symptoms, repeat the test in 4 to 6 weeks after removing NSAIDs and PPIs and ruling out recent infection. If two consecutive readings remain elevated, that pattern warrants endoscopy.

For people with diagnosed IBD, a single rise above 250 in remission is a reason to call your gastroenterologist and discuss therapy adjustment, ideally before symptoms return. Pairing the result with a CRP (blood inflammation marker) and basic labs gives the fullest picture.