Calprotectin is a protein found in neutrophils, a type of white blood cell. When inflammation occurs, particularly in the gastrointestinal tract, these neutrophils migrate to the inflamed area and release calprotectin. This release makes calprotectin a valuable marker for detecting the presence of inflammation. Elevated levels of calprotectin in stool samples indicate that inflammation is present, though they do not pinpoint the exact cause or location of that inflammation.
Calprotectin’s Role in the Body
Calprotectin is a complex of two proteins (S100A8 and S100A9) that makes up a significant portion of neutrophil protein content. These neutrophils release calprotectin when they are activated and migrate to sites of inflammation, especially in the lining of the gut. The protein has anti-inflammatory and antimicrobial properties, playing a role in immune regulation and maintaining intestinal balance. Its stability in stool samples makes fecal calprotectin a particularly useful and non-invasive indicator for intestinal inflammation. This stability means it resists degradation as it passes through the digestive system, allowing for accurate measurement. Measuring calprotectin levels helps distinguish between inflammatory conditions, which require further investigation, and non-inflammatory conditions, such as irritable bowel syndrome (IBS), where levels are typically normal.
Inflammatory Bowel Diseases
Inflammatory Bowel Diseases (IBD), primarily Crohn’s disease and ulcerative colitis, are chronic conditions characterized by persistent inflammation in the gastrointestinal tract. These diseases are among the most common causes of significantly elevated calprotectin levels. The ongoing inflammatory processes in IBD lead to a substantial influx of neutrophils into the bowel, which in turn release large quantities of calprotectin into the gut lumen.
In newly diagnosed IBD, calprotectin concentrations can be high, reflecting inflammation severity. For instance, levels exceeding 250 µg/g are often associated with active inflammation in IBD. Calprotectin is frequently used in the diagnosis of IBD, helping to differentiate it from non-inflammatory conditions like IBS, where calprotectin levels are typically much lower. Beyond initial diagnosis, calprotectin levels monitor disease activity in individuals with IBD. Changes in calprotectin levels can indicate whether the disease is in remission or experiencing a flare-up. It also helps predict the risk of relapse and assess the effectiveness of ongoing treatments, potentially reducing the need for more invasive procedures like colonoscopy to evaluate mucosal healing.
Other Gastrointestinal Conditions
While Inflammatory Bowel Diseases are a primary cause, various other gastrointestinal conditions can also lead to elevated calprotectin levels. Infectious gastroenteritis, caused by bacterial, viral, or parasitic infections, is a common reason for increased calprotectin. Bacterial infections, such as those from Salmonella or Clostridioides difficile, often result in substantially high calprotectin levels, while viral infections typically lead to lower, though still elevated, concentrations compared to healthy individuals. These elevations are usually temporary and resolve once the infection clears.
Celiac disease, an immune reaction to gluten that causes inflammation in the small intestine, can also elevate calprotectin levels. In untreated celiac disease, calprotectin concentrations correlate with the degree of intestinal mucosal damage and tend to normalize with a gluten-free diet. Microscopic colitis (collagenous and lymphocytic colitis) can also elevate calprotectin levels.
Diverticulitis, an inflammation of small pouches that can form in the lining of the intestine, can also cause increased fecal calprotectin. Higher calprotectin values are seen in diverticulitis. The levels often correlate with the inflammatory infiltrate and can decrease after appropriate treatment.
Non-Gastrointestinal and Temporary Factors
Elevated calprotectin levels are not exclusively indicative of chronic gut diseases; various non-gastrointestinal and temporary factors can also contribute to an increase. Certain medications, such as non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, can cause irritation and low-grade inflammation in the intestinal lining, leading to a rise in calprotectin. This effect typically resolves once the medication is discontinued.
Systemic inflammatory conditions like rheumatoid arthritis or psoriasis may also elevate calprotectin, even without gut inflammation. Recent strenuous physical exercise can also cause a temporary increase in calprotectin levels. Minor, transient inflammation, even in otherwise healthy individuals, can also lead to slight elevations. These non-gastrointestinal and temporary causes generally result in less dramatic elevations compared to conditions like IBD.
Interpreting Your Results
A high calprotectin result indicates the presence of inflammation in the intestines and requires further investigation by a healthcare professional. The level of elevation indicates inflammation severity, with higher values suggesting more significant inflammation. However, calprotectin is a sensitive marker and can be falsely elevated, so a repeat test may be requested.
Your doctor will consider the calprotectin level in conjunction with your symptoms, medical history, and other diagnostic test results to determine the underlying cause. This comprehensive approach helps guide the next steps, which may include additional diagnostic tests like endoscopy or colonoscopy to directly visualize the intestinal lining and obtain tissue samples for definitive diagnosis. A normal or low calprotectin level generally suggests that symptoms are likely due to a non-inflammatory bowel disorder, potentially avoiding the need for invasive procedures.