If you have been asked to collect a stool sample for a faecal calprotectin test, you may be wondering what it measures and why your doctor has requested it. This test is now one of the most widely used non-invasive tools for detecting gut inflammation, particularly in people with suspected or known inflammatory bowel disease (IBD). Understanding what calprotectin is and what the results mean can help you make sense of your symptoms and guide conversations with your healthcare team.
What is faecal calprotectin?
Calprotectin is a protein released by neutrophils, a type of white blood cell that forms part of the body’s innate immune system. When the lining of your gut is inflamed, neutrophils migrate into the intestinal tissue and release calprotectin into the stool. Because calprotectin is stable in faeces and easy to measure, it serves as a reliable marker of inflammation in the gastrointestinal tract.
The test itself is simple. A small stool sample is collected at home, sent to a laboratory, and analysed for the concentration of calprotectin. Results are typically reported in micrograms per gram of stool.
Why the test matters in IBD
Faecal calprotectin is particularly useful in inflammatory bowel disease because it can distinguish between inflammatory conditions, such as Crohn’s disease and ulcerative colitis, and non-inflammatory conditions, such as irritable bowel syndrome (IBS). This distinction is important because symptoms like diarrhoea, abdominal pain, and bloating can overlap between these conditions, but the underlying causes and treatments are very different.
In people with established IBD, calprotectin levels can reflect disease activity even when symptoms are mild or absent. This makes the test valuable for monitoring remission, detecting early signs of relapse, and assessing whether treatment is working.
How calprotectin reflects gut inflammation
Neutrophil activity
When the gut lining is inflamed, immune cells are recruited to the site of injury. Neutrophils are among the first responders, releasing calprotectin as part of the inflammatory response. The more active the inflammation, the higher the concentration of calprotectin in the stool.
Correlation with endoscopic findings
Studies have shown that faecal calprotectin levels correlate well with findings on colonoscopy, the gold standard for assessing mucosal inflammation. Elevated calprotectin often indicates active ulceration or inflammation visible on endoscopy, while low levels suggest mucosal healing. This allows doctors to assess disease activity without requiring invasive procedures every time.
Sensitivity to mucosal healing
Mucosal healing, the resolution of inflammation and ulceration in the gut lining, is a key treatment goal in IBD. Faecal calprotectin is sensitive to this process, and falling levels over time can indicate that treatment is effective and the gut is healing. Conversely, rising levels may signal a flare even before symptoms become noticeable.
Interpreting your results
Faecal calprotectin levels are usually categorised into ranges, though exact thresholds vary between laboratories. In general, a level below 50 micrograms per gram is considered normal and suggests that significant intestinal inflammation is unlikely. Levels between 50 and 150 are often regarded as borderline and may prompt further investigation or repeat testing. Levels above 150 are typically associated with active inflammation and warrant clinical review.
It is important to note that calprotectin is not specific to IBD. Other conditions that cause gut inflammation, such as infections, colorectal cancer, and non-steroidal anti-inflammatory drug (NSAID) use, can also raise levels. Your doctor will interpret the result in the context of your symptoms, medical history, and other tests.
When the test is used
Diagnosis
Faecal calprotectin is often used as an initial screening tool when IBD is suspected. A normal result can help rule out inflammatory bowel disease and avoid unnecessary endoscopy in people whose symptoms are more likely due to IBS or other functional disorders.
Monitoring disease activity
Once IBD is diagnosed, calprotectin testing can monitor disease activity over time. Regular testing allows your healthcare team to detect early signs of relapse, adjust treatment, and assess whether you are in remission. This is particularly helpful in people who do not always experience symptoms when inflammation is present.
Assessing treatment response
After starting or changing treatment, calprotectin levels can help determine whether the therapy is working. A fall in calprotectin suggests that inflammation is improving, while persistently high or rising levels may indicate that a different approach is needed.
Limitations of the test
While faecal calprotectin is a useful tool, it is not perfect. Some people with active IBD may have normal or only mildly elevated levels, particularly if inflammation is confined to a small area or located in the upper gastrointestinal tract. The test also cannot distinguish between Crohn’s disease and ulcerative colitis, nor can it pinpoint the exact location of inflammation.
Calprotectin levels can fluctuate for reasons unrelated to IBD, including gastrointestinal infections, dietary factors, and medication use. A single raised result does not always mean a flare, and a single normal result does not guarantee remission. Results should always be interpreted alongside clinical assessment and, where appropriate, imaging or endoscopy.
What to do with your result
If your calprotectin is elevated, your doctor may recommend further investigation, such as colonoscopy, imaging, or blood tests, to assess the extent and severity of inflammation. If you are already being treated for IBD, an elevated result may prompt a review of your current therapy.
If your result is normal, this is reassuring, but it does not rule out all gut conditions. Symptoms such as pain, bloating, or changes in bowel habit should still be discussed with your healthcare team, as other causes may need to be explored.
Calprotectin testing is a tool, not a diagnosis. It provides useful information, but it is most effective when used as part of a broader clinical picture.
Practical takeaways
- Faecal calprotectin measures a protein released by immune cells during gut inflammation.
- The test can help distinguish between inflammatory conditions like IBD and non-inflammatory conditions like IBS.
- Elevated levels often indicate active inflammation, but the result must be interpreted in context.
- The test is useful for monitoring disease activity, detecting early relapse, and assessing treatment response.
- Other conditions, including infections and medication use, can also raise calprotectin levels.
- Discuss your result with your healthcare team to understand what it means for your individual situation.
Conclusion
The faecal calprotectin test offers a practical, non-invasive way to assess inflammation in the gut. For people with IBD, it provides valuable insight into disease activity and treatment response, often without the need for repeated endoscopy. While it is not a standalone diagnostic tool, it plays an important role in managing gut health over time. If you have questions about your result or what it means for your treatment, your gastroenterology team is the best source of guidance.
References
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This article is intended for informational and educational purposes only. It does not constitute medical advice and should not be used as a substitute for professional medical guidance, diagnosis, or treatment.