What does a fecal calprotectin test measure?

From the Guidelines

A fecal calprotectin test measures the level of calprotectin, a protein released by white blood cells called neutrophils, in a stool sample, and is used to detect inflammation in the intestines, particularly in patients with inflammatory bowel diseases (IBD) like Crohn's disease and ulcerative colitis. This test is non-invasive and requires only a small stool sample that can be collected at home using a provided container, then sent to a laboratory for analysis.

Key Points

• Normal calprotectin levels are typically below 50 micrograms per gram of stool, with levels between 50-120 μg/g considered borderline, and levels above 120 μg/g suggesting active inflammation, as supported by a recent study 1.
• The test works because during intestinal inflammation, neutrophils migrate to the inflamed area and release calprotectin, which then appears in the stool in proportion to the severity of inflammation.
• A more recent study 1 suggests that a calprotectin level of less than 150 ± 50 mg/g can reliably rule out active inflammation, although this may not be the case in patients with mild symptoms.
• It is essential to consider the limitations of the test, including inter- and intra-assay test variability, and inter-individual heterogeneity in biomarker responsiveness, as highlighted in a 2023 guideline 1.
• The fecal calprotectin test is a valuable tool for distinguishing between inflammatory conditions like IBD and non-inflammatory conditions like irritable bowel syndrome (IBS), as well as for monitoring treatment effectiveness in patients with known IBD.

Clinical Considerations

• When interpreting fecal calprotectin results, it is crucial to consider the clinical context, including the patient's symptoms, medical history, and treatment plan.
• A single measurement of fecal calprotectin may not be sufficient, and repeat testing or endoscopic evaluation may be required to confirm the results, especially in cases of borderline or unexpected results.
• The test performance thresholds, including acceptable false positive and false negative rates, may vary depending on the treatment adjustment being considered, and should be guided by downstream implications, as noted in the 2023 guideline 1.

From the Research

Fecal Calprotectin Test

• The fecal calprotectin test measures the level of calprotectin in stool, which is a protein found in neutrophil granulocytes 2.
• Calprotectin is a marker of intestinal inflammation, and elevated levels can indicate the presence of inflammatory bowel disease (IBD) [(2,3)].
• The test is non-invasive and can be used to differentiate IBD from functional conditions such as irritable bowel syndrome [(2,4)].

What the Test Measures

• The fecal calprotectin test measures the concentration of calprotectin in stool, which correlates with the level of intestinal inflammation [(2,5)].
• The test can be used to monitor disease activity and response to therapy in patients with IBD [(6,3)].
• Elevated levels of calprotectin can also be seen in other conditions, such as gastrointestinal infections and celiac disease 4.

Clinical Applications

• The fecal calprotectin test can be used as a screening tool to identify patients with a low probability of IBD 4.
• The test can also be used to differentiate disease relapse from functional symptoms in patients with IBD 4.
• The accuracy of the test for predicting endoscopic activity in patients with IBD has been demonstrated, with a high area under the ROC curve 5.