Fecal Calprotectin Testing Overview of Procedure, Interpretation, and Clinical Utility
How does the test work?
The fecal calprotectin test works by simply measuring the amount of calprotectin protein in a stool sample. An increased level of calprotectin in stool indicates the presence of inflammation in the gastrointestinal tract. During inflammation in IBD, there is an increased migration of neutrophils to the inflammatory sites in the digestive tract. These neutrophils release elevated amounts of calprotectin protein. The protein then leaves the body through stool. By measuring its concentration, doctors can estimate the amount of inflammation present.
Test procedure
The test procedure is very simple and non-invasive. To perform the test, the patient needs to collect a small sample of stool, usually about half a teaspoon, and bring it to the doctor. The sample is then sent to a laboratory for analysis. In the laboratory, technician use an immunoassay technique to detect and quantify the amount of calprotectin protein present in the stool sample. The results are usually reported in micrograms of calprotectin per 1 gram of stool sample (μg/g).
Result interpretation
The fecal calprotectin test results help doctors in interpreting the level of inflammation in the gut. Normal calprotectin levels in stool are usually below 50 μg/g. Levels between 50-100 μg/g indicate mild inflammation, 100-200 μg/g indicate moderate inflammation and above 200 μg/g indicate severe inflammation. Higher calprotectin levels are seen in conditions with active inflammation like ulcerative colitis compared to those with no or minimal disease activity. The test results also help monitor response to treatment. Decreased levels after treatment indicate reduction in gut inflammation.
Uses and applications
There are several important uses and applications of fecal calprotectin testing in clinical practice:
Diagnosis of IBD: Higher Fecal Calprotectin Test levels have good correlation with endoscopic and histological evidence of intestinal inflammation seen in IBD conditions like Crohn's disease and ulcerative colitis. The test helps distinguish IBD from irritable bowel syndrome which usually has normal calprotectin levels.
Monitoring response to treatment: Fecal calprotectin levels are monitored in patients undergoing treatment for IBD. Falling levels after therapy indicate effectiveness of the treatment in reducing inflammation. Rising levels may suggest worsening disease activity requiring changes in management.
Detection of relapse: Elevated calprotectin levels can detect relapse or return of disease activity in IBD patients even before clinical symptoms appear. This helps doctors initiate early treatment interventions.
Post-surgical recurrence monitoring: The test is useful to detect recurrence or return of inflammation in the digestive tract after surgery for IBD conditions like Crohn's disease.
Differential diagnosis of abdominal pain: It assists in differentiating IBD from other colon disorders or infections presenting with similar abdominal pain symptoms like diverticulitis.
Advantages and limitations
The key advantages of fecal calprotectin test are its non-invasive nature, objective measurement of gut inflammation levels, ability to differentiate IBD from IBS and monitor response to therapies. However, the test also has some limitations. Other intestinal conditions like infections, medications and foods can also cause a transient rise in calprotectin not necessarily indicating IBD. False negative results are possible during periods of mild or quiescent disease. Concurrent anal fissures or hemorrhoids may yield inaccurate high readings. Despite limitations, it is considered a highly useful first-line test for evaluation of IBD and monitoring of its clinical course.
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