Calprotectin: Structure, Location, Function and Clinical Utility

It is a protein with calcium and zinc bonds, which has antimicrobial properties and is abundantly located in the body.

Calprotectin has bacteriostatic and mycotic properties comparable to those of antibiotics. It is located in the stool, cells, plasma, and body fluids.

Therefore, the abundance of calprotectin in granulocytes and neutrophils and their antimicrobial activity indicate an essential role in the organism’s defense.

It works as a protein biomarker since it is present in the stool when intestinal inflammation occurs.

Among the advantages of this protein is that it is not affected by medications.

It is resistant to the activity of digestive enzymes (unlike other fecal markers); it does not change before inflammation and systemic infection.

The fecal calprotectin test avoids the need for unnecessary endoscopic procedures in many patients.


As a marker, it has greater sensitivity and specificity than other serological markers, such as CRP and ESR, and is stable at room temperature for up to 7 days (the high calcium content is responsible for this unusual stability).


Calprotectin (CP) is a 36 kDa protein abundant in the human body, characterized by a low molecular weight dimeric acid protein (36.5 kDa).

It is calcium fixative and 100% soluble in saturated solutions of ammonium sulfate, properties that classify them as S100. Its structure consists of a light polypeptide chain and two heavy chains.


It is found mainly in neutrophil polymorphonuclear leukocytes (PMNs) and, to a lesser extent, in monocytes and reactive macrophages.

There is a high level of calprotectin in the extracellular fluid obtained during the affliction of various inflammatory conditions, such as cystic fibrosis, rheumatoid arthritis, abscesses, and the presence of malignant diseases.

When inflammation occurs in the intestines, the intestinal mucosa is filled with neutrophils.

These cross the mucosa to the intestinal lumen, where its rupture (lysis) originates, releasing calprotectin, which appears in the stool where it can be detected and quantified.


The findings indicate that calprotectin has a regulatory activity in inflammatory processes.

It is also indicated that it may hurt the fibroblasts in high concentrations and intervene in the recovery of the inflammatory tissue.

Calprotectin can be released from activated leukocytes and concentrated in the urine, saliva, stool, plasma, serum, cerebrospinal fluid, and synovial fluid.

This concentration increases during the onset of bacterial infections or inflammation of organs.

At present, there are several biomarkers of inflammatory bowel disease.

Usually, acute phase reactants were used as a diagnostic aid to evaluating intestinal inflammation and the use of antibodies to discriminate between Ulcerative Colitis and Crohn’s Disease.

Non-intestinal diseases may influence the systemic markers used above.

They have very low sensitivity and specificity to reveal the existence of intestinal inflammation, and their correlation is poor concerning the activity indexes.

Currently, fecal markers are an innovative diagnostic tool that can evaluate intestinal inflammation in a rapid, reproducible, simple, and non-invasive way.

Of all these markers, the fecal calprotectin stands out since it correlates with its concentration the number of polymorphonuclear leukocytes in the intestinal lumen, revealing the level of inflammation.

Clinical utility

To obtain the calprotectin values, a sample collection is performed:

Blood samples:

The laboratory makes blood samples in ethylenediaminetetraacetic acid (EDTA chemical substance that adheres to the ions of certain elements such as calcium); the serum concentration is higher and has more variations.

These samples are used since substantial amounts of calprotectin are released during coagulation.

Body fluids:

Fluids are high concentrations in response to infections and inflammations in the body.

The plasma levels of calprotectin indicate the activity of the disease in rheumatoid arthritis.

Stool samples:

Calprotectin plasma concentrations are high in diseases related to increased neutrophil activity.

When inflammation of the intestinal wall occurs, the granulocytes migrate through this wall so that calprotectin is also detectable in the stool.

Several investigations reveal that fecal calprotectin increases significantly in intestinal diseases such as ulcerative colitis, Crohn’s disease, inflammatory bowel disease, and colon cancer.

CalproLab, Calprotectin, or CalproSmart are used in laboratory tests to determine fecal calprotectin concentrations.

This has become a non-invasive routine test to reveal gastrointestinal inflammation or neoplasia and to assess activity in inflammatory bowel diseases and the response it offers to treat.

Also, thanks to this marker, the risk of relapse in patients in clinical remission can be predicted; the presence of an average calprotectin value is confident that mucosal recovery has been achieved.

Calprotectin has diagnostic specificity for:

  • Intestinal Inflammatory Disease.
  • Recurrent abdominal pain, chronic nonspecific diarrhea, and infant colic.
  • Monitoring of the treatment of Inflammatory Bowel Disease and prediction of relapse.