Calprotectin  a 36 kDa protein present in neutrophil cytoplasm, has antimicrobial and apoptosis inducing activities, which are reversed by the addition of zinc. Calprotectin is a calcium-binding protein secreted predominantly by neutrophils and monocytes. Fecal calprotectin is a marker for neoplasic and inflammatory gastrointestinal diseases. Calprotectin is an abundant neutrophil protein found in both plasma and stool that is markedly elevated in infectious and inflammatory conditions, including inflammatory bowel disease (IBD). In vitro studies have shown that calprotectin inhibits the growth of various microorganisms.

Calprotectin is a calcium-binding protein with in vitro bacteriostatic and fungistatic properties. It is found in abundance in neutrophils, where it accounts for 60% of the protein in the cytosol; lower concentrations are found in monocytes and reactive macrophages. It was hoped that measurement of faecal calprotectin would represent a surrogate marker of neutrophil influx into the bowel lumen and in turn act as a marker of intestinal inflammation. Studies to date support this hypothesis; increased levels of faecal calprotectin are found in inflammatory bowel disease, colonic cancer and non-steroidal anti-inflammatory drug (NSAID) treatment, suggesting it is a sensitive but non-specific marker of intestinal inflammation.

Fecal calprotectin (FC) has been proposed as a marker of inflammatory bowel disease (IBD), but few studies have evaluated its usefulness in patients with chronic diarrhea of various causes. The usefulness of measuring the faecal concentration of calprotectin, a neutrophil-derived protein, in the non-invasive diagnosis and management of inflammatory bowel disease and other gut disorders has been investigated for some years both in adults and children.  It is often difficult to distinguish between irritable bowel syndrome and chronic inflammatory bowel disease. This leads in many cases to extensive and unnecessary colonoscopic examinations. The calprotectin test allows clear differentiation between the two patient groups. Fecal calprotectin levels correlate significantly with histologic and endoscopic assessment of disease activity in Morbus Crohn's disease and ulcerative colitis as well as with the fecal excretion of indium-111-labelled neutrophilic granulocytes that has been suggested as the “gold standard“ of disease activity in inflammatory bowel disease. However, measuring 111-indium-labeled granulocytes is very costly (patient’s hospitalization, analysis and disposal of isotopic material) and is connected with radioactive exposure of the patients. For this reason, a repeated application to children and pregnant women is not recommended.

Faecal calprotectin (FC), a novel marker of intestinal inflammation, may play a role in clarifying the presence of pathology, reducing the need for endoscopy in some patients, and may also provide good prognostic information. Calprotectin is a 36kDa protein comprising one light and two heavy chains. This cytosolic protein is found in neutrophils and certain macrophage subtypes (CD14+) but is not present in T or B lymphocytes. Reference ranges for fecal calprotectin have been established in healthy adults and children, and elevated concentrations of fecal calprotectin have been demonstrated in numerous studies of patients with IBD. Fecal calprotectin correlates well with histological inflammation as detected by colonoscopy with biopsies and has been shown successfully to predict relapses and detect pouchitis in patients with IBD. Fecal calprotectin has been shown to consistently differentiate IBD from irritable bowel syndrome because it has excellent negative predictive value in ruling out IBD in undiagnosed, symptomatic patients. Fecal calprotectin also may be useful in determining whether clinical symptoms in patients with known IBD are caused by disease flares or noninflammatory complications/underlying irritable bowel syndrome and in providing objective evidence of response to treatment.

Calprotectin is an abundant cytosolic protein complex of human neutrophils with in vitro extracellular antimicrobial activity. Studies suggest that calprotectin may be actively secreted from intact HL-60 cells and that it can be translocated to polymorphonuclear neutrophil (PMN) cell membranes. Specifically, the increase in extracellular calprotectin correlated directly with a proportional decrease in PMN viability.

Elevated levels of calprotectin are a much better predictor of relapse than standard inflammatory markers (CRP, ESR HB). Comparing this marker with standard fecal occult blood screening in colorectal cancer demonstrates clearly the diagnostic advantages of the fecal calprotectin test.