Fecal calprotectin is a commonly used, non-invasive biomarker that assesses inflammation within the gastrointestinal tract. Doctors frequently use this simple stool test to differentiate between inflammatory conditions, such as Inflammatory Bowel Disease (IBD), and non-inflammatory conditions, like Irritable Bowel Syndrome (IBS). A high result signals the presence of intestinal inflammation, suggesting further investigation is necessary to identify the source of irritation.
The Function of Calprotectin
Calprotectin is a protein originating primarily from neutrophils, a type of white blood cell. Neutrophils are the body’s first responders, rapidly migrating to any site of infection or inflammation. This protein makes up a large percentage of the total protein found within these immune cells.
When the gut lining becomes inflamed, neutrophils rush to the area. These cells release their contents, including large amounts of calprotectin, into the intestinal lumen. The calprotectin is then excreted in the stool, making it a stable and measurable indicator of active inflammation in the digestive tract.
Measuring calprotectin in the feces is advantageous because it directly reflects processes happening within the gut lining, unlike blood markers that indicate systemic inflammation. The concentration detected in the stool is proportional to the number of neutrophils that have migrated into the gastrointestinal mucosa. This direct correlation makes it a valuable tool for objectively assessing the severity of intestinal inflammation.
Interpreting Fecal Calprotectin Levels
Fecal calprotectin levels are typically reported in micrograms of calprotectin per gram of stool (\(\mu g/g\)). Although specific cut-off points vary between laboratory assays, there are generally accepted ranges for interpretation. A result below \(50\ \mu g/g\) is usually considered normal and strongly suggests the absence of significant intestinal inflammation, making an inflammatory bowel condition unlikely.
Levels between \(50\ \mu g/g\) and \(100\ \mu g/g\) are often seen as a borderline zone, indicating mild or low-level inflammation. This range is common in individuals with non-inflammatory disorders like Irritable Bowel Syndrome or may be due to temporary causes. In these intermediate cases, doctors may recommend repeating the test after a few weeks to monitor the trend.
A result exceeding \(100\ \mu g/g\) generally indicates active mucosal inflammation that warrants further clinical investigation. Levels above \(250\ \mu g/g\) are highly suggestive of active Inflammatory Bowel Disease. For patients with concerning symptoms, this higher range significantly increases the likelihood of a condition causing structural damage to the bowel lining.
Why Calprotectin Levels Become Elevated
Calprotectin levels become elevated whenever there is a substantial presence of neutrophils in the gastrointestinal tract. The most significant cause of very high and sustained elevation is Inflammatory Bowel Disease (IBD), including Crohn’s Disease and Ulcerative Colitis. Active IBD leads to chronic inflammation and high neutrophil migration, often resulting in levels well over \(500\ \mu g/g\).
A high result does not exclusively indicate IBD, as the test is sensitive to any gut inflammation. Infectious colitis caused by bacteria or viruses, such as Salmonella or Clostridioides difficile, can lead to a significant, transient elevation. These infections cause acute, intense inflammation, but the calprotectin level should normalize once the infection clears.
Other, less severe causes can lead to moderate elevation, generally in the \(100\ \mu g/g\) to \(300\ \mu g/g\) range. The use of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), such as ibuprofen, can irritate the gut lining and cause a rise in calprotectin. Other conditions that may elevate the marker include diverticulitis, microscopic colitis, and certain types of colorectal cancer.
Next Steps After a High Result
An elevated calprotectin result acts as a screening tool, indicating inflammation rather than providing a definitive diagnosis. The next step is to consult with a gastroenterologist, a doctor specializing in digestive health, for a comprehensive evaluation. This specialist interprets the result in the context of the patient’s symptoms, medical history, and other blood tests.
For a significantly high result, particularly one above \(250\ \mu g/g\), the gastroenterologist typically recommends follow-up diagnostic procedures. Endoscopy or colonoscopy is often required to visually inspect the intestinal lining, confirm the extent of inflammation, and obtain tissue samples (biopsies) for a conclusive diagnosis. The calprotectin test helps prioritize which patients need these more invasive procedures.
Beyond initial diagnosis, the test is routinely used to monitor patients already diagnosed with IBD. Decreasing calprotectin levels suggest that treatment is working and the patient is achieving mucosal healing. Conversely, a rising level in a patient in clinical remission may signal a disease flare-up, prompting the doctor to adjust medication or initiate further investigation.