Fecal Calprotectin: Normal Range, High Results and Whether It Is IBS or Bowel Inflammation

Calprotectin is a calcium- and zinc-binding protein derived mainly from the cytoplasm of neutrophils, the white blood cells that take part in the first line of the inflammatory response. It has direct antimicrobial activity and takes part in regulating the innate immune response. When inflammation develops in the bowel wall, neutrophils migrate into the bowel lumen, where they die and release calprotectin. The concentration of calprotectin in stool is therefore related to the intensity of mucosal inflammation (review by Kapel et al., 2023). According to the review by Ricciuto and Griffiths (2019), the concentration in stool is many times higher than in blood, which makes it easy to measure.

Calprotectin is thus not a marker of any specific disease, only a marker of neutrophils in the bowel lumen. This is an important distinction: a rise means inflammation (inflammatory bowel disease, bacterial or parasitic infection, drug-induced inflammation, sometimes a tumor), but does not by itself say which. No rise, on the other hand, means active mucosal inflammation is most likely absent and symptoms have another background, most often functional. This asymmetry, the much greater value of a negative than of a positive result, is the key to using the test sensibly.

The test is performed on a stool sample, usually a few grams placed in a special container. The result is given in micrograms per gram of stool (µg/g, equivalent to mg/kg). Laboratory methods (ELISA, immunoturbidimetry, rapid tests) differ from one another and do not always give identical numbers, so decision thresholds should always be related to the reference range given by the particular laboratory, and follow-up measurements performed with the same method.

These numbers are worth translating into practical language. A negative predictive value of 99.8% means that with a low calprotectin the chance that a patient with IBS-like symptoms actually has inflammatory bowel disease is very small (about 1 in 500 at an assumed prevalence of 1%). That is why the test is so useful as a first filter: it lets most patients be managed as IBS without colonoscopy. A positive predictive value of 9%, in turn, means that at the same disease prevalence only about 1 in 11 people with a positive result truly has IBD. The rest are false-positive results that need clarifying, but in most cases do not mean serious disease.

Dependence on disease prevalence is a basic rule of every diagnostic test. In a specialist's office, where patients with a stronger suspicion of IBD are referred, the positive predictive value will be higher; in primary care, where most have IBS, lower. That is why the same number, say 120 µg/g, can mean something different in a 25-year-old with blood in the stool and weight loss than in a 40-year-old woman with bloating after meals who has taken reflux medication for years.

There is no single universal normal value. It is most often assumed that a value below 50 µg/g is normal (negative), the range from roughly 50 to 100-200 µg/g is a so-called grey zone that needs clinical interpretation and often repeating, and values above 200-250 µg/g point to significant inflammation. Laboratories, however, use their own thresholds that depend on the method, so you should always look at the reference range printed on the result. The boundaries between categories are not sharp; it is more a continuum of probability.

Study data confirm that the 50 µg/g threshold is sensitive but not very specific. In a prospective study in 15 centers in China of 556 patients with chronic diarrhea (Liu et al., 2026), the optimal cut-off for detecting colonoscopic abnormalities was 93.8 µg/g (AUC 0.830), for colorectal inflammation 118.4 µg/g (AUC 0.896), and for inflammatory bowel disease 157.0 µg/g (AUC 0.929). This means the more specific the disease sought, the more a higher threshold improves accuracy, whereas a lower one increases sensitivity at the cost of false alarms. The test also had limited ability to detect high-risk adenomas (AUC 0.587), a reminder that it is not meant for finding polyps.

It is also worth knowing that in healthy people the result does not always fall below 50 µg/g. In a Swedish cohort of 382 healthy people aged 50-65 (Fall et al., 2017), the calculated reference intervals were below 199 µg/g for one extraction method and below 153 µg/g for the other, well above the classic 50 µg/g threshold. The authors stress that values depend on the sample-preparation method. This is another reason not to treat a single, slightly raised result as a diagnosis.

The most common cause of a non-specific calprotectin rise is medication. In a cross-sectional study of 590 people referred for colonoscopy whose examination turned out normal (Lundgren et al., 2019), as many as 36% had calprotectin above 50 µg/g. In multivariable analysis a raised value was associated with age (adjusted OR 1.05 per year), proton pump inhibitors (OR 3.84; 95% CI 2.34-6.32), nonsteroidal anti-inflammatory drugs (OR 2.41; 95% CI 1.16-5.00) and acetylsalicylic acid (OR 2.93). The relationship was confirmed by a 2025 Swedish observational study of 431 patients with IBS or functional bowel disorders (Sandberg-Janzon and Karling): in people with a recent PPI prescription the median was 66 vs 23 µg/g in the others, and for NSAIDs 57 vs 25 µg/g. A result above 50 µg/g was also associated with more frequent referral for colonoscopy (40% vs 19%), which the authors assess as potentially unnecessary investigations.

A second source of confusion is biological variability. In an older, small study by Husebye et al. (2001) of 14 people without inflammation or tumor who each gave eight stool samples before colonoscopy, in 36% the values were consistently low (below 50 µg/g), while in 64% they fluctuated from day to day, also above that threshold (mean 70 µg/g, single results from 9 to 461, within-patient standard deviation 52 µg/g). The authors found no explanation in the history or the colonoscopy findings. The practical conclusion: a single moderately raised result in a person without alarm features often deserves repeating rather than immediate escalation.

In practice calprotectin is used as a decision gate. With lower gastrointestinal symptoms in a person under 45-50 without alarm features, a low result allows the patient to be managed as IBS, while a high result (especially above 200-250 µg/g) justifies referral to a gastroenterologist and most often colonoscopy with biopsies. A result in the grey zone needs repeating and consideration of medicines. The JAMA review of chronic noninfectious diarrhea (Singh et al., 2026) recommends that evaluation of chronic diarrhea include testing for celiac disease and calprotectin, and colonoscopy (along with upper endoscopy) in people with gastrointestinal bleeding, unexplained weight loss, age 45 or older, nocturnal diarrhea, steatorrhea or iron deficiency anemia.

Calprotectin and the FIT test (fecal occult blood) answer different questions and do not replace each other. FIT detects blood, mainly from tumors and large polyps; calprotectin detects inflammation. In a British study of 654 patients referred with suspected colorectal cancer (Turvill et al., 2016), the negative predictive value of calprotectin for cancer was 98.6%, and 27.8% of patients had a normal result and could in theory have been spared the urgent diagnostic pathway, but the positive predictive value for cancer was low. In a retrospective study of 669 patients (Perry et al., 2026), calprotectin above 50 µg/g had high sensitivity for IBD both in people aged 18-49 (94.1%) and in those aged 50 and over (93.8%), but the positive predictive value was only 20.9% and 12.8%, and in the 50+ group the FIT test detected organic pathology, including cancer, better than calprotectin at a threshold of 150 µg/g. The authors suggest a role for calprotectin as a rule-out test in people over 50 with lower gastrointestinal symptoms and a negative FIT when cancer is not suspected.

A simple conclusion follows from these data: in older people, those with alarm symptoms or a family history of colorectal cancer, you must not stop at a normal calprotectin. The test supports decisions well in younger patients with IBS-like symptoms, but it is not a screening tool for cancer. Colonoscopy or the FIT test are used for screening, and we write about them separately.

The reverse mistake is also common: since the result is above normal, it must be Crohn's disease. In reality, as we saw, as many as 34-36% of people with a normal colonoscopy may have a result above 50 µg/g, mainly because of age and medicines. That is why the number only has value when set against the clinical context.

See a doctor without delay if, along with bowel complaints, there is blood in the stool or black stools, unintentional weight loss, fever, diarrhea that wakes you at night, anemia or iron deficiency, severe and worsening abdominal pain, symptoms appearing for the first time after age 45-50, or a family history of colorectal cancer, inflammatory bowel disease or celiac disease. Such situations call for clinical assessment regardless of the calprotectin result.

Calprotectin is one of the few tests that really changes management: it lets us spare invasive diagnostics to those who do not need them and send those who do to a specialist sooner. The most harm comes from interpreting it without context: as a verdict after one slightly raised result, or as a guarantee of health after a normal result in someone with alarm features. If you take PPIs or NSAIDs, tell your doctor before the result takes on a life of its own.