High Fecal Calprotectin: Causes and What to Do Next

A high fecal calprotectin (FC) result signals inflammation somewhere in the gastrointestinal tract, most commonly in the intestines. The test measures a protein released by a specific type of white blood cell that floods into gut tissue during an inflammatory process, and its main clinical use is distinguishing inflammatory bowel disease (IBD) from functional conditions like irritable bowel syndrome (IBS). But a raised level does not automatically mean IBD, and several other conditions, medications, and even your age can push the number up. Understanding what drives the result and what comes next can save you from unnecessary worry or, conversely, prompt the right follow-up before a treatable condition progresses.

What the Test Actually Measures

Calprotectin is a protein that binds calcium and zinc, and it belongs to a family of proteins found mainly inside neutrophils, the immune cells your body sends to fight infection and inflammation. When the lining of the gut becomes inflamed for any reason, neutrophils migrate into the intestinal wall and spill their contents into the space where stool is forming. The calprotectin they release is remarkably stable in feces, surviving days at room temperature, which is part of why the test works so well as a practical screening tool.¹ Because the protein resists degradation, a small stool sample collected at home and mailed to a lab can give a reliable snapshot of intestinal inflammation without any invasive procedure.²

The key thing to remember is that fecal calprotectin is not disease-specific. It tells you that neutrophils are active in your gut; it does not tell you why. That “why” is the entire clinical question, and it’s why a high result almost always leads to further investigation rather than a diagnosis on its own.

What Counts as a High Result

Most laboratories use a three-tier system. A result below 50 micrograms per gram of stool is considered negative, a result between 50 and 120 is borderline, and anything above 120 is positive and suggests clinically meaningful inflammation.³ Some labs use slightly different cutoffs, and the specific assay your lab uses matters because there is no universally accepted standard method for measuring FC. Different manufacturers’ kits can give somewhat different numbers for the same sample.⁴ If you’re comparing results over time, try to have them run on the same assay platform at the same lab whenever possible.

As a rough guide, levels in active Crohn’s disease or ulcerative colitis commonly run into the hundreds or even above 1,000 micrograms per gram. Mildly elevated results in the 50 to 200 range are more ambiguous and require careful clinical interpretation. Very high levels, say above 500, make IBD or another serious inflammatory process much more likely, though even then confirmation by endoscopy is the standard.

Inflammatory Bowel Disease Is the Primary Concern

The test was developed largely to help doctors decide who really needs a colonoscopy among patients with chronic gut symptoms. A systematic review and economic evaluation found that at a cutoff of 50 micrograms per gram, fecal calprotectin distinguished IBD from IBS with a pooled sensitivity of about 93% and specificity of about 94%.⁵ A more recent meta-analysis of 17 studies covering nearly 2,000 patients reported slightly lower but still strong numbers: roughly 86% sensitivity and 92% specificity.⁶ In practical terms, if your FC is clearly below 50, the chance that your symptoms are caused by IBD is very small. This is where the test’s real power lies: its ability to rule IBD out and spare you a colonoscopy.

The flip side is that a positive result does not rule IBD in with the same confidence. When the background prevalence of IBD in the tested population is low, even a good test produces many false positives relative to true positives. That same meta-analysis calculated that at a 1% IBD prevalence, the positive predictive value was only about 9%, meaning roughly 9 out of 10 people with a positive test in that low-prevalence setting would not turn out to have IBD.⁶ This is an important point to absorb if you’re reading a high result on your lab report and panicking. A high FC is a reason to investigate further, not a diagnosis.

Other Intestinal Conditions That Raise Calprotectin

Because the test picks up neutrophil activity in the gut rather than a specific disease, a range of non-IBD conditions can push levels above normal.

Infections: Bacterial gastroenteritis from organisms like Salmonella, Campylobacter, or Clostridioides difficile causes intense neutrophilic inflammation. FC levels during acute gut infections can rival those seen in active IBD. If your symptoms started suddenly, your doctor will likely check for infectious causes before pursuing an IBD workup.
Microscopic colitis: This condition causes chronic watery diarrhea but looks normal on standard colonoscopy until biopsies are taken. A meta-analysis found that patients with microscopic colitis had moderately elevated calprotectin levels compared to healthy controls.⁷ The elevations tend to be more modest than in classic IBD, but there is overlap.
Diverticulitis: Acute diverticulitis, where a small pouch in the colon wall becomes inflamed or infected, causes localized inflammation that neutrophils rush to address. During a flare, FC can be elevated.
Celiac disease: Some patients with active celiac disease have mildly raised FC levels, reflecting small-bowel inflammation. The elevations are usually lower than in IBD and normalize with a gluten-free diet.

Medications That Inflate the Number

This is one of the most underappreciated causes of a falsely elevated result. If you take nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, naproxen, or diclofenac regularly, your calprotectin may be elevated even if your gut is otherwise healthy. A study of over 300 patients on NSAIDs found that nearly half had evidence of NSAID-related small-bowel inflammation, and their calprotectin levels were significantly higher than those of controls.⁸ This was independent of which NSAID was taken or the dose.

Proton pump inhibitors (PPIs), the acid-suppressing drugs commonly prescribed for reflux, also appear to raise FC. In one observational study of patients with functional bowel disorders, those with a PPI prescription within 90 days of the test had median FC levels roughly three times higher than those without, and NSAID users showed a similar pattern.⁹ A cross-sectional study in patients referred for colonoscopy confirmed these associations, finding that PPI use nearly quadrupled the odds of an elevated FC, and NSAID and aspirin use roughly doubled or tripled the odds.¹⁰

If you are taking any of these medications and receive an unexpectedly high FC result, it is worth discussing with your doctor whether a medication washout and retest might clarify the picture before committing to a colonoscopy. This is not always practical, but in borderline cases it can be very helpful.

Colorectal Cancer and Polyps

A high calprotectin level can also reflect colorectal cancer. In a study comparing calprotectin to the traditional fecal occult blood test, 90% of patients with colorectal carcinoma had elevated calprotectin, versus only 58% who had a positive occult blood test. For adenomatous polyps, which are precancerous growths, calprotectin detected about 55% compared to just 10% with fecal occult blood.¹¹ The inflammation around colorectal tumors actively recruits neutrophils, and tissue studies have shown that calprotectin concentrations in carcinoma and adenoma samples are several times higher than in healthy surrounding mucosa.¹²

This does not mean FC is used as a primary colorectal cancer screening tool. Screening programs typically rely on fecal immunochemical tests (FIT) or colonoscopy. But the possibility of cancer is one reason doctors take a persistently high FC seriously, especially in patients over 50 or those with red-flag symptoms like unexplained weight loss, rectal bleeding, or a change in bowel habits.

Why Age Makes a Difference

If you’re interpreting a child’s result using the standard adult cutoff of 50 micrograms per gram, you may be set up for confusion. Healthy infants and young children have naturally higher calprotectin levels than adults, and the numbers drop gradually with age. One study of children aged 1 to 18 months found that babies under 6 months had high FC levels as a matter of course, and even between 6 and 18 months, levels remained higher than those of children over 4 years old.¹³ Another study confirmed a strong negative correlation between age and FC in healthy children, with the youngest children showing the highest levels.¹⁴

The practical consequence: applying adult reference ranges to infants will generate a stream of false positives. Pediatric gastroenterologists are aware of this, but primary care providers or anxious parents looking at a lab printout may not be. If your infant has an elevated FC, it warrants a conversation with a pediatrician who understands age-adjusted norms before anyone starts worrying about IBD.

On the other end of the age spectrum, older adults also tend to have slightly higher baseline FC levels than younger adults. The cross-sectional study that found associations with PPI and NSAID use also identified age itself as an independent predictor of elevated FC.¹⁰ This makes sense given the higher prevalence of subclinical gut inflammation and medication use in older populations.

Monitoring Known IBD

For patients who already have a Crohn’s disease or ulcerative colitis diagnosis, fecal calprotectin takes on a different role. Instead of screening, it becomes a monitoring tool, offering a noninvasive way to check whether the disease is flaring, responding to treatment, or headed toward relapse. FC has demonstrated strong performance for this purpose, tracking disease activity and predicting flares before symptoms return.¹⁵

Lower FC levels in IBD patients correlate with the presence of mucosal healing on endoscopy. One study found that patients whose colonoscopies showed healed mucosa had a median FC of about 69 micrograms per gram, while those with ongoing mucosal inflammation had a median of about 481.¹⁶ The gap is large enough that serial FC measurements can serve as a practical stand-in for repeat colonoscopies in many cases, helping doctors decide when to step up treatment and when it’s safe to ease off.¹⁷

For predicting relapse specifically, a meta-analysis of 24 studies found that FC performed reasonably well, with an optimal cutoff around 152 micrograms per gram and corresponding sensitivity and specificity each around 72 to 74%.¹⁸ In pediatric Crohn’s disease, FC showed good accuracy for predicting relapse within three months of sample collection.¹⁹ The trend in your results matters at least as much as any single number. A steadily climbing FC, even if each individual result is only modestly elevated, can be a meaningful early warning.

What Happens After a High Result

The next step depends heavily on context. Your doctor will consider your symptoms, age, medication use, family history, and how high the result actually is. In general, the pathway looks something like this:

Borderline result (50 to 120): Often warrants a repeat test after addressing confounders. If you’re taking NSAIDs or a PPI, stopping them temporarily (if safe) and retesting a few weeks later can clarify the picture.
Clearly elevated (above 120 to 200): Infectious causes should be ruled out with stool cultures and a C. difficile test. If those are negative and the elevation persists, referral to a gastroenterologist for possible endoscopy is typical.
Very high (above 500): This level of inflammation usually prompts a more urgent referral. Colonoscopy with biopsies is the standard next step to look for IBD, microscopic colitis, or other structural disease.

The real value of FC testing in this pathway is economic and practical. Using calprotectin as a pre-endoscopic screening tool has been estimated to reduce colonoscopy demand by roughly 50% at a 50-microgram-per-gram cutoff, saving health systems substantial costs while avoiding unnecessary invasive procedures for patients whose symptoms are functional.²⁰ Combining FC with a fecal occult blood test can reduce colonoscopies by about 39% while cutting total diagnostic costs by roughly a fifth.²¹

Getting an Accurate Sample

An encouraging feature of the test is that stool consistency does not appear to significantly affect results across modern assay platforms.²² Whether your sample is formed or loose, the extraction and measurement process handles it reliably. That said, variability between different manufacturers’ assays remains a real issue. An international consensus effort has acknowledged that each step of the measurement process can influence the result, and no single method has been universally adopted as a standard.⁴

For the most useful results, try to collect the sample during a symptomatic period if the goal is diagnosis, and avoid taking NSAIDs for a few days beforehand if you can safely do so. If the sample sits at home for a day or two before reaching the lab, it is generally still valid, though following the kit’s instructions on storage is worth the effort.

Elevated Calprotectin in Autoimmune and Rheumatic Conditions

The gut is not the only place that can drive a high FC result. Some systemic conditions cause subclinical gut inflammation that patients may not even feel. In systemic sclerosis, a connective tissue disease that can affect the skin and internal organs, roughly 38% of newly diagnosed patients had elevated fecal calprotectin, compared to only about 7% of healthy controls.²³ This suggests that gut inflammation may be present early in the disease course, even before GI symptoms become apparent.

Ankylosing spondylitis, a type of inflammatory arthritis primarily affecting the spine, shows a particularly striking pattern. Two-thirds of patients in one longitudinal study had FC above 50 at both the initial visit and the five-year follow-up. Calprotectin correlated with disease activity scores and inflammatory blood markers. Critically, much of this elevation was attributable to NSAID use: when patients stopped NSAIDs for three weeks, their FC dropped by a median of 116 micrograms per kilogram.²⁴ This makes ankylosing spondylitis a perfect example of how the NSAID confounding effect and the disease’s own inflammatory tendencies overlap, making FC results harder to interpret in these patients.

The Link Between Gut Inflammation and Mental Health

An emerging area of research involves the relationship between fecal calprotectin levels and depression in IBD patients. In a study of IBD patients evaluated with standardized depression questionnaires, those with mild to moderately severe depression had significantly higher calprotectin levels than those with minimal depression, with a roughly threefold difference in median values. Calprotectin correlated with specific depressive symptoms, including fatigue, sleep disorders, and slowed movement. The researchers found that calprotectin was an independent predictor of depression even after accounting for other variables.²⁵

This does not mean that gut inflammation directly causes depression, or that treating inflammation will resolve mood symptoms. The gut-brain axis involves complex bidirectional signaling, and fatigue or pain from a flare can contribute to low mood through straightforward quality-of-life pathways. But it does reinforce the idea that a high FC in an IBD patient is not just a number to track for bowel health. If you have IBD and notice worsening fatigue, sleep problems, or mood changes alongside a rising calprotectin, those symptoms deserve attention in their own right, not just as afterthoughts to a GI flare.