Fecal calprotectin testing is a non-invasive medical tool used to investigate symptoms of chronic digestive distress, such as persistent diarrhea and abdominal pain. The test measures the amount of a protein called calprotectin in a stool sample, which acts as a reliable marker for inflammation within the gastrointestinal tract. Calprotectin is released by a specific type of white blood cell, called a neutrophil, when the lining of the intestine is irritated or damaged. Determining the level of this protein helps medical professionals distinguish between conditions that involve organic inflammation and those that are primarily functional in nature.
Understanding Fecal Calprotectin Testing
Calprotectin is a complex protein structure, specifically an S100A8/A9 heterodimer, that is highly concentrated within the cytoplasm of neutrophils. When inflammation occurs in the gut, these neutrophils migrate to the affected intestinal lining to fight perceived threats or repair damage. The presence of this immune response causes the neutrophils to release their contents, including calprotectin, which then passes into the stool.
Measuring fecal calprotectin provides a quantifiable assessment of intestinal inflammation. Because calprotectin is resistant to degradation by digestive enzymes, its concentration in the stool correlates directly with the migration of inflammatory cells into the intestinal lumen. The test involves a simple stool sample collection analyzed in a laboratory, typically using enzyme-linked immunosorbent assay (ELISA). This procedure is a valuable initial screening tool, often helping to determine whether more invasive procedures, such as a colonoscopy, are warranted.
Interpreting Elevated Calprotectin Levels
A result from a fecal calprotectin test is generally reported in micrograms of calprotectin per gram of stool (\(\mu\)g/g). The interpretation of these results is typically divided into three broad zones, though specific laboratory reference ranges can vary. A low or normal result, usually defined as less than 50 \(\mu\)g/g, suggests that symptoms are likely due to a non-inflammatory cause, such as Irritable Bowel Syndrome (IBS).
Results in the moderate or “gray” zone, commonly between 50 \(\mu\)g/g and 200 \(\mu\)g/g, indicate low-grade inflammation. This level may necessitate a repeat test or a deeper look at other potential causes, as it is not strongly indicative of a chronic inflammatory condition. A result above 200 \(\mu\)g/g, or sometimes above 250 \(\mu\)g/g, is considered high and suggests the presence of an active, organic inflammatory disease in the gastrointestinal tract.
The concentration of calprotectin exhibits a dose-response relationship with the severity of inflammation. Higher levels correlate with more widespread or intense inflammation within the bowel. For instance, levels exceeding 600 \(\mu\)g/g suggest significant inflammatory activity. This quantitative measure helps doctors gauge the severity of the inflammatory process before a definitive diagnosis is established.
Conditions Associated with High Results
The most significant cause of a persistently high fecal calprotectin level is Inflammatory Bowel Disease (IBD), which includes Crohn’s disease and Ulcerative Colitis. These chronic conditions are characterized by ongoing inflammation that causes tissue damage in the digestive tract. In acute flares of IBD, calprotectin levels can often exceed 250 \(\mu\)g/g, sometimes reaching levels in the thousands.
A high calprotectin result provides a distinction between IBD and Irritable Bowel Syndrome (IBS), a functional disorder. Unlike IBD, IBS does not involve the chronic inflammation or tissue destruction that causes the sustained release of calprotectin. Therefore, a normal or mildly elevated reading points toward IBS, helping to avoid unnecessary invasive testing.
Other inflammatory conditions can also cause elevated calprotectin levels, though typically not as high as those seen in active IBD. These include infectious colitis, caused by pathogens like Salmonella or Clostridioides difficile, which trigger a strong but temporary immune response. Untreated celiac disease, microscopic colitis, and diverticulitis are also known to raise the protein’s concentration in stool.
Certain external factors and medications can also lead to temporary elevations. The regular use of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), such as ibuprofen or aspirin, can cause low-grade intestinal irritation (enteropathy), leading to a rise in calprotectin. Rigorous physical exercise or the presence of colorectal cancer can occasionally elevate levels, necessitating investigation, especially in older patients.
Next Steps Following a High Reading
A significantly high fecal calprotectin result prompts follow-up procedures to confirm the source of the inflammation. The patient is typically referred to a gastroenterologist for further evaluation. For a moderate result, the initial step may involve repeating the test after stopping medications, like NSAIDs or proton pump inhibitors, that could cause a false elevation.
For persistently high results, definitive diagnostic steps involve direct visualization of the intestinal lining. Endoscopic procedures, primarily colonoscopy, are necessary to examine the tissue and collect biopsies for a conclusive diagnosis. These procedures confirm the presence, location, and severity of the disease, allowing the medical team to tailor an appropriate long-term treatment plan.