What Is Calprotectin in Stool and What Does It Mean?

Calprotectin is a protein released by white blood cells, and when it shows up at elevated levels in a stool sample, it signals that the intestinal lining is inflamed. Doctors order the test primarily to help sort out whether gut symptoms like chronic diarrhea, cramping, or bloating stem from an inflammatory condition such as Crohn’s disease or ulcerative colitis, or from a functional problem like irritable bowel syndrome that doesn’t involve visible tissue damage. The distinction matters enormously because the treatment paths, and the urgency, are completely different. But the number on the lab report is not as straightforward as “high means bad, low means fine,” and understanding the nuances can save you both anxiety and unnecessary procedures.

What Calprotectin Actually Is

Calprotectin is a small protein that binds calcium and zinc, and it makes up roughly 60 percent of the protein content inside a type of white blood cell called a neutrophil. When neutrophils rush to a site of inflammation in the gut wall, calprotectin gets released into the intestinal lumen and eventually ends up in stool. It’s part of the body’s innate immune defense: by grabbing hold of essential metals like zinc and manganese, calprotectin starves bacteria and fungi of the nutrients they need to grow.¹ Experiments have confirmed this directly: when researchers mutated calprotectin so it could no longer bind those metals, it lost its ability to inhibit microbial growth.²

Once outside the cell, calprotectin also acts as a signaling molecule, activating receptors on other immune cells and amplifying the inflammatory response.³ This dual role as both an antimicrobial weapon and an inflammatory amplifier is what makes it such a useful marker. The more inflamed your intestinal lining is, the more neutrophils migrate there, the more calprotectin floods into the gut, and the more ends up in your stool. It’s a remarkably direct measurement of what’s happening to the tissue.

One practical advantage over blood tests: calprotectin is tough. It resists breakdown by gut enzymes and remains stable in stool for days, which makes it well suited for a test that patients collect at home and mail or bring to a lab.⁴

Why Doctors Order the Test

The single most common reason for a fecal calprotectin test is to help decide whether someone with persistent gut symptoms needs a colonoscopy or other invasive workup. Irritable bowel syndrome is extremely common, and its symptoms overlap heavily with inflammatory bowel disease (IBD). Without a way to screen, many people with IBS would undergo colonoscopies they don’t need, while some with early IBD might wait too long.

A large meta-analysis pooling data from 17 studies and nearly 2,000 patients found that fecal calprotectin distinguished IBD from IBS with about 86 percent sensitivity and 92 percent specificity.⁵ In practical terms, a normal calprotectin result makes IBD very unlikely, and a clearly elevated one pushes the clinician toward endoscopy. A separate meta-analysis estimated that using calprotectin as a screening step could cut the number of adults needing endoscopy by about two-thirds, at the cost of a delayed diagnosis in roughly 6 percent of IBD cases due to false negatives.⁶ That trade-off is generally considered favorable, especially because the savings in unnecessary procedures and patient discomfort are substantial, with one analysis finding that calprotectin screening saved over $400 per adult patient.⁷

Reading the Numbers

Most labs report calprotectin in micrograms per gram of stool (µg/g). The commonly used threshold for adults is 50 µg/g, meaning results below that are considered normal, but interpretation in clinical practice is more layered than a single cutoff suggests. Many gastroenterologists work with a “traffic light” mental model:

• Below 50 µg/g: Intestinal inflammation is unlikely. IBD is improbable, though not impossible.
• 50 to 150–200 µg/g: A gray zone. Mild elevation could reflect a minor infection, medication effect, or early inflammatory disease. Retesting in a few weeks or further investigation is typical.
• Above 200–250 µg/g: Significant intestinal inflammation is probable, and endoscopic evaluation is usually warranted.

These thresholds shift depending on the clinical question. For detecting small bowel Crohn’s disease, a cutoff of 100 µg/g performed better overall than 50 µg/g, balancing sensitivity and specificity more evenly.⁸ For distinguishing ulcerative colitis from IBS-type diarrhea, one study found a cutoff around 188 µg/g most useful.⁹ The point is that no single number works perfectly for every scenario, and your doctor will interpret the result in the context of your symptoms, history, and other test findings.

Monitoring IBD and Predicting Flares

Beyond initial diagnosis, calprotectin has become one of the most valuable tools for managing established IBD. People with Crohn’s disease or ulcerative colitis often feel reasonably well even when low-grade inflammation is quietly damaging their intestinal lining. Calprotectin can detect that subclinical inflammation before symptoms return, giving clinicians a window to adjust treatment proactively rather than reactively.

In patients who appear to be in remission, a calprotectin level below roughly 170 µg/g strongly correlates with mucosal healing on endoscopy. One study found that patients with mucosal healing had a median calprotectin around 69 µg/g, compared to about 481 µg/g in those with ongoing inflammation.¹⁰ Similarly, in ulcerative colitis, a level below about 158 µg/g predicted complete mucosal healing with 90 percent sensitivity and 85 percent specificity.⁹

For predicting flares, a meta-analysis across 24 studies identified an optimal cutoff around 152 µg/g, with sensitivity and specificity both hovering near 72–74 percent.¹¹ An earlier meta-analysis of prospective studies found slightly higher pooled sensitivity (78 percent) and specificity (73 percent) for relapse prediction.¹² These numbers aren’t perfect, but they’re good enough to guide clinical decisions and potentially spare patients from frequent colonoscopies just to check on disease activity. Think of serial calprotectin measurements as a kind of thermostat for gut inflammation: you track the trend over time, and a rising number prompts closer attention even if you feel fine.

Non-IBD Reasons Calprotectin Can Be Elevated

A high calprotectin result does not automatically mean IBD. Any condition that sends neutrophils into the gut wall will raise levels. This is one of the most important things to understand before panicking over a lab result.

Infections are a common cause. Bacterial gut infections produce substantially elevated calprotectin, and the levels tend to correlate with how sick you are.¹³ In one multicenter study, fecal calprotectin detected acute bacterial diarrhea with about 83 percent sensitivity and 87 percent specificity.¹⁴ If you had a stomach bug last week and then got a calprotectin test, the number could still be elevated.

Medications are another frequent culprit. Anti-inflammatory painkillers (NSAIDs) are well known to damage the gut lining. In one study of over 300 patients taking NSAIDs, calprotectin levels were significantly higher than in controls, with 44 percent showing evidence of NSAID-related gut injury.¹⁵ Proton pump inhibitors (PPIs), the widely prescribed acid-suppressing drugs, were also independently associated with elevated calprotectin, with users having nearly four times the odds of a level above 50 µg/g. Aspirin showed a similar though smaller effect.¹⁶ If your doctor is interpreting a borderline result, they will want to know what medications you’re taking.

Celiac disease can raise calprotectin as well. Newly diagnosed celiac patients in one study had median calprotectin levels around 117 µg/g, which dropped to roughly 4 µg/g after starting a strict gluten-free diet.¹⁷ Colorectal cancer and precancerous polyps can also elevate levels. Patients with colorectal cancer had elevated calprotectin about 90 percent of the time, which was considerably more reliable than the traditional fecal occult blood test for that purpose.¹⁸ A systematic review confirmed that calprotectin levels are significantly elevated in both polyp and cancer groups compared to healthy controls.¹⁹ Even gastrointestinal bleeding from an upper source (like an ulcer) can mildly raise calprotectin, though it takes a large volume of blood loss to push the number above 200 µg/g.²⁰

Why Results Can Vary From Sample to Sample

One of the less discussed aspects of calprotectin testing is that the number you get can fluctuate quite a bit, even within the same day. In patients with active ulcerative colitis, the median within-day variation was around 40 percent, with some individuals showing swings from low to high across different bowel movements in a single 24-hour period.²¹ Another study in active UC patients found a median individual coefficient of variation of 52 percent, and observed that levels tended to be higher when more time had passed since the previous bowel movement.²²

For this reason, the first stool of the morning is often recommended as the most representative sample, though the evidence on this is mixed: in one study it contained the highest calprotectin value a third of the time and the lowest value about equally as often.²¹ What clinicians take from this variability is that a single result near a cutoff boundary shouldn’t be treated as gospel. Trends over time are more informative than any one measurement.

Storage conditions matter too. Calprotectin concentrations decline when stool sits at room temperature, with a significant drop possible after just one day in unextracted samples. Refrigerating the sample or using an extraction device can preserve accuracy for several days.²³ If you’re collecting a sample at home, follow the lab’s instructions for storage and delivery timing closely.

Children and Infants Are a Special Case

If your pediatrician ordered a calprotectin test for your baby or toddler and the number came back high, don’t assume something is wrong. Healthy infants naturally have much higher fecal calprotectin levels than adults, and this declines gradually with age. Babies under six months can have levels several times the adult upper limit without any disease.²⁴ The levels continue to drop through toddlerhood: in one cohort, the 95th percentile fell from 135 µg/g at 7–12 months to just 12 µg/g by ages 37–48 months.²⁵ Adult reference ranges generally become applicable around age four.

This makes interpreting the test in young children tricky. A value of 100 µg/g in a three-month-old could be perfectly normal, while the same number in a ten-year-old would be noteworthy. Researchers have called for age-specific reference ranges in pediatric practice, but these aren’t yet standardized everywhere.²⁶ If your child’s result seems concerning, asking whether age-appropriate cutoffs were used is a reasonable question for the doctor.

How Calprotectin Compares to Blood Tests

You might wonder why stool needs to be tested at all when a simple blood draw can measure C-reactive protein (CRP) and other inflammatory markers. The answer is specificity. CRP rises with inflammation anywhere in the body: a sore throat, a sprained ankle, or a dental infection can all bump it up. Calprotectin is far more specific to the gut because it’s measured at the site of potential inflammation. Studies have found that fecal calprotectin has higher sensitivity than CRP for diagnosing IBD.²⁷

Lactoferrin is another stool marker sometimes compared to calprotectin. Both are released by neutrophils, and their diagnostic performance for intestinal inflammation is very similar. One study comparing them head-to-head found overall sensitivity and specificity of about 78 and 83 percent for calprotectin versus 80 and 85 percent for lactoferrin.²⁸ A more recent evaluation found the two were roughly equivalent for detecting remission in ulcerative colitis, with calprotectin having a slight edge.²⁹ Calprotectin has become the dominant test in clinical practice partly because it’s been studied more extensively and partly because its stability in stool makes the logistics of testing easier.

Point-of-Care and At-Home Testing

Traditional calprotectin testing uses a lab-based method called ELISA, which takes hours to run and requires sending your sample to a central laboratory. Faster point-of-care tests have become available, including some designed for use in a doctor’s office during an appointment. These rapid tests correlate well with ELISA results when calprotectin levels are in the lower-to-moderate range (below about 250 µg/g), but the agreement weakens at higher levels.³⁰ For the typical screening question of “is inflammation present or not,” that’s usually good enough. For precise monitoring of disease activity in someone with known IBD, your gastroenterologist may prefer the lab-based test. It’s also worth knowing that different commercial assays can give somewhat different absolute values for the same sample, which is one reason clinicians focus on trends rather than single numbers, and ideally use the same assay brand consistently for any given patient.

What an Elevated Result Does Not Tell You

Calprotectin is excellent at confirming that inflammation is present in the gut, but it cannot tell you what is causing that inflammation. A reading of 500 µg/g could mean a Crohn’s flare, a severe bacterial infection, ulcerative colitis, or advanced colorectal cancer. Additional testing, often endoscopy with biopsies, is almost always needed to pin down the diagnosis. Similarly, calprotectin doesn’t specify where in the gastrointestinal tract the inflammation sits. Inflammation in the colon, small intestine, or even stomach can all raise levels, though the test is most sensitive to inflammation in the lower GI tract.

Age is another confounding factor beyond childhood. Older adults tend to have slightly higher baseline calprotectin levels, and the medications older adults commonly use, such as NSAIDs, aspirin, and PPIs, further push numbers up.¹⁶ A mildly elevated result in an 80-year-old on multiple medications means something different from the same number in a 25-year-old who takes nothing.

The test also has limited value in conditions that don’t involve neutrophilic inflammation. Microscopic colitis, for instance, involves a different pattern of immune cell infiltration, and calprotectin levels can be normal or only mildly elevated despite active symptoms. Functional disorders like IBS, by definition, don’t produce intestinal inflammation, so calprotectin is expected to be normal. That’s a feature, not a bug: it’s precisely this ability to confirm the absence of inflammation that makes the test useful as a gatekeeper.

Celiac Disease and Diet-Related Shifts

Calprotectin can reflect the intestinal damage caused by celiac disease, though the elevations tend to be more modest than those seen in IBD. In newly diagnosed celiac patients, levels often sit in the mildly-to-moderately elevated range, and they come down after the person starts a gluten-free diet.³¹ One study found the drop was dramatic, from a median of about 117 µg/g at diagnosis to roughly 4 µg/g after dietary adherence normalized antibody levels.¹⁷ This raises the possibility of using calprotectin to monitor whether the gluten-free diet is effectively healing the gut, though it’s not standard practice for that purpose yet.

For people without a diagnosed condition, normal dietary variation does not meaningfully change calprotectin. A spicy meal or a day of unusual eating won’t spike your levels the way it might briefly disrupt your digestion. The test is responsive to actual tissue-level inflammation, not to transient digestive stress.