Fecal calprotectin measurement is a widely used, non-invasive method to assess inflammation within the gastrointestinal (GI) tract. This test quantifies a specific protein found in a stool sample. An elevated level suggests an active inflammatory process is occurring in the intestines. Doctors use this result as a preliminary screening tool to guide decisions regarding the need for more invasive diagnostic procedures for patients presenting with chronic digestive symptoms.
The Biological Function of Calprotectin
Calprotectin is a calcium- and zinc-binding protein predominantly found within a type of white blood cell called a neutrophil. Neutrophils are a core part of the immune system and are among the first responders to sites of inflammation or infection in the body. When the lining of the intestine becomes inflamed, these immune cells migrate from the bloodstream into the gut tissue to combat the perceived threat.
As neutrophils break down, they release their internal contents, including calprotectin, into the intestinal lumen. Because the protein is highly resistant to degradation by bacterial enzymes, it remains stable and is easily measured in the stool sample. The concentration detected in the feces directly correlates with the number of neutrophils that have entered the GI tract and the overall level of intestinal inflammation.
Conditions Indicated by Elevated Calprotectin
An elevated fecal calprotectin result indicates active inflammation somewhere along the digestive tract. The degree of elevation helps clinicians differentiate between possible causes, ranging from severe chronic conditions to temporary issues. Levels below approximately 50 micrograms per gram (µg/g) are considered normal, making significant intestinal inflammation unlikely.
A high calprotectin level, often defined as exceeding 150 µg/g or sometimes 250 µg/g, is suggestive of Inflammatory Bowel Disease (IBD). This includes chronic conditions such as Crohn’s disease and Ulcerative Colitis, where the body’s immune system mistakenly attacks the GI tract. The primary utility of the test is to distinguish these inflammatory diseases from non-inflammatory functional disorders like Irritable Bowel Syndrome (IBS).
Patients with IBS typically have calprotectin levels within the normal range, allowing doctors to avoid unnecessary invasive procedures. However, moderate elevations, generally falling between 50 and 150 µg/g, represent a gray area and do not automatically confirm IBD. These moderate results can be caused by transient factors such as infectious gastroenteritis, where the gut is temporarily inflamed by a pathogen. Other potential causes of mild to moderate elevation include the use of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) or some forms of colorectal cancer.
Clinical Management Following a High Result
A significantly elevated calprotectin level necessitates further investigation to pinpoint the cause of intestinal inflammation. The next step often involves a colonoscopy and biopsy, allowing a doctor to visually inspect the bowel lining and collect tissue samples. This invasive procedure is the standard for confirming Inflammatory Bowel Disease (IBD) and assessing the disease extent.
For patients already diagnosed with IBD, calprotectin testing moves from a diagnostic tool to a monitoring device. Measuring the protein regularly helps track how active the disease is, which is often a more objective measure than symptoms alone. A drop in calprotectin levels after starting treatment suggests that the medication is effectively reducing inflammation and promoting mucosal healing in the gut lining.
Calprotectin also serves as a predictor of disease course. Consistently high levels in patients who are otherwise feeling well can signal a higher risk of a future relapse, allowing doctors to proactively adjust treatment to prevent a severe flare-up. If a patient’s initial calprotectin is only mildly elevated, the doctor may choose to retest the stool sample after a few weeks. A return to normal levels suggests a temporary cause rather than a chronic condition.