What is Fecal Calprotectin Test?
Fecal calprotectin is a protein found in the cytosol of neutrophils (a type of white blood cell) that makes up about 60% of the total protein content of neutrophils. When there is inflammation in the digestive tract, neutrophils migrate to the affected site. Some neutrophils undergoing apoptosis or necrosis release calprotectin. Higher levels of calprotectin in the stool (feces) can therefore indicate intestinal inflammation. The fecal calprotectin test measures the level of calprotectin in a stool sample to help diagnose and monitor inflammatory bowel diseases like Crohn's disease and ulcerative colitis.
Why the test is done?
The fecal calprotectin test is usually done to:
- Help diagnose inflammatory bowel disease (IBD). Higher levels of calprotectin are found in the stool of individuals with active IBD compared to healthy individuals. This test can help differentiate IBD from irritable bowel syndrome which does not cause inflammation.
- Monitor disease activity and treatment response in known cases of IBD. Calprotectin levels tend to correlate with the severity of intestinal inflammation. Monitoring calprotectin levels can help determine if the disease treatment is effective in reducing inflammation over time.
- Screen for postoperative recurrence of Crohn's disease. Calprotectin levels can identify early signs of recurrence after surgery before clinical symptoms appear.
- Investigate other causes of abdominal pain and changes in bowel habits when inflammatory bowel disease is suspected but tests like colonoscopy are inconclusive.
- Monitor immune-mediated gastrointestinal disorders like ulcerative proctitis for response to treatment.
The test is not done as a generic screening test for intestinal disorders but as a supplementary test to endoscopy, imaging, or clinical symptoms. It serves as a non-invasive marker of intestinal inflammation.
How is it performed?
The Fecal Calprotectin Test is a very simple and painless test to perform. To collect the stool sample, the individual is given a plastic container or a special collection kit with instructions. A small amount of stool equivalent to half a teaspoon is scooped directly from the toilet or stool using a spatula or wooden tongue depressor provided and sealed in the container.
The stool sample needs to be brought to the lab or doctor's office within one day of collection for testing. If needed, the sample can be stored briefly in the refrigerator before testing. No special preparation or diet is required prior to collecting the stool sample. The lab then performs various quantitative tests like enzyme-linked immunosorbent assay (ELISA) on the stool sample to measure the concentration of calprotectin.
Test results and their interpretation
The fecal calprotectin levels are reported either as micrograms of calprotectin per gram of stool (μg/g) or as nanomoles of calprotectin per liter of stool (nmol/l).
- Less than 50 μg/g is considered negative or normal with no significant intestinal inflammation.
- 50-150 μg/g is considered a "gray zone" - may or may not indicate mild inflammation.
- Above 150 μg/g is positive for significant intestinal inflammation. Higher the level, more severe the inflammation is likely to be.
- Levels above 250-300 μg/g are strongly suggestive of active inflammatory bowel disease.
- Monitoring levels and seeing them drop below 150 μg/g with treatment indicates reduction in inflammation.
- Persistently elevated levels despite treatment may require changes to therapy.
- A rising calprotectin level on treatment could flag worsening of disease or treatment failure.
Limitations of the test
- A positive or high calprotectin result does not pinpoint the specific cause or location of inflammation. Endoscopy may still be needed.
- Other non-inflammatory intestinal conditions like infections, celiac disease, or cancer can sometimes cause mildly elevated results.
- Transient inflammation from foods, medications or infections may result in temporary elevations.
- Results can be normal in people with Crohn's disease confined purely to the small intestine or during periods of remission.
- Levels may get elevated temporarily after intensive anti-inflammatory treatment due to neutrophil death and release of calprotectin.
- Collection and handling errors leading to bacterial contamination can potentially skew results.
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