Calprotectin is a protein released by neutrophils, a primary type of white blood cell that responds to injury, infection, and inflammation. The Fecal Calprotectin Test (FCP) is a non-invasive tool that measures the concentration of this protein in a stool sample. A high level of calprotectin in the feces reliably indicates inflammation within the gastrointestinal tract. Medical professionals frequently use this test to determine if a patient’s digestive symptoms are caused by an inflammatory condition.
Understanding How Calprotectin Levels Rise
The presence of calprotectin in the stool results from the body’s defense mechanism responding to damage or irritation in the gut lining. When intestinal tissue is injured by disease or a pathogen, the immune system initiates an inflammatory response. Neutrophils migrate from the bloodstream into the compromised area and release their contents, including large amounts of calprotectin. Because this protein is stable and resistant to degradation, the concentration measured in the stool acts as a proxy for the number of neutrophils that have entered the gut. The higher the measured calprotectin level, the greater the degree of active inflammation in the intestines.
Primary Chronic Causes of High Calprotectin
The most recognized cause of persistently high calprotectin levels is Inflammatory Bowel Disease (IBD). IBD is a group of chronic, autoimmune conditions, including Ulcerative Colitis (UC) and Crohn’s Disease (CD). These diseases cause long-term, destructive inflammation of the digestive tract, leading to a sustained influx of neutrophils and elevated calprotectin.
In patients with active IBD, calprotectin levels are often very high, frequently exceeding 250 micrograms per gram of stool. The test is useful for differentiating IBD from functional disorders like Irritable Bowel Syndrome (IBS), where symptoms are similar but inflammation is typically absent. The degree of calprotectin elevation often correlates closely with the severity of mucosal damage observed during an endoscopy.
For individuals diagnosed with IBD, the FCP test is a tool for monitoring disease activity. Tracking these protein levels non-invasively allows physicians to assess treatment effectiveness and whether medication is achieving mucosal healing. A significant increase in calprotectin levels may predict a clinical relapse or flare-up of the disease several months before symptoms appear. This predictive capability helps guide treatment adjustments to prevent future flares.
Other Significant Gastrointestinal Causes
While IBD is a chronic cause, several other conditions can cause a temporary or localized spike in fecal calprotectin. Acute infections, particularly those caused by bacteria like Salmonella or Clostridioides difficile, trigger a rapid and intense neutrophil response in the gut. These infectious causes often result in extremely high calprotectin levels, but they usually return to normal once the infection is successfully treated and cleared from the body.
Another common source of elevated calprotectin is the effect of certain medications on the intestinal lining. Nonsteroidal Anti-inflammatory Drugs (NSAIDs), such as ibuprofen or naproxen, can damage the protective barrier of the gut, leading to low-grade inflammation known as NSAID enteropathy. This drug-induced injury causes neutrophils to gather and release calprotectin, resulting in a moderate elevation that typically resolves quickly once the offending medication is discontinued.
Other organic diseases that cause inflammation within the digestive tract can also lead to elevated results. Diverticulitis, which involves the inflammation of pouches in the colon wall, can cause a localized rise in calprotectin. Untreated Celiac disease results in elevated levels that tend to normalize once a strict gluten-free diet is adopted. Colorectal cancer can also be associated with increased calprotectin due to localized inflammation and ulceration around the tumor site.
Non-Disease Factors Influencing Results
Some non-pathological factors can lead to a minor or moderate elevation in calprotectin, which is important to consider during result interpretation. Infants and very young children naturally exhibit higher calprotectin levels compared to older children and adults. This is thought to be related to the normal development and maturation of the gut immune system.
Strenuous physical activity, such as long-distance running, temporarily increases intestinal permeability and causes transient, low-level inflammation. Obtaining a stool sample immediately following an intense workout may result in a slightly elevated calprotectin reading that is not indicative of a chronic disease.
Any source of blood contamination in the stool sample, such as from hemorrhoids or a minor anal fissure, can also artificially raise the result because the blood contains neutrophils. Minor, transient inflammation from a brief viral illness or intestinal stress can also cause a temporary spike in the protein level.
Because of these various influences, a single elevated calprotectin result is rarely diagnostic on its own. The test is always interpreted by a physician in the context of a patient’s overall symptoms, medical history, and the results of other diagnostic procedures to determine the true cause of the elevation.