Calprotectin is a calcium- and zinc-binding protein which is predominantly present in the cytoplasm of cells involved in pathogen defence, such as neutrophil granulocytes, monocytes and macrophages. In neutrophil granulocytes it accounts for as much as 60% of the cytosolic protein. In intestinal inflammation neutrophil granulocytes migrate through the intestinal wall into the intestinal lumen, which leads to an elevated calprotectin level in the stool. The level of faecal calprotectin correlates directly with the number of neutrophil granulocytes in the intestinal lumen and is thus specifically elevated in inflammatory bowel diseases (IBD), such as Crohn's disease and ulcerative colitis, and to a much smaller extent in other entities such as neoplasia and polyps. Faecal calprotectin measurement is an easy, non-invasive first line test which clearly differentiates IBD from IBS (irritable bowel syndrome) and other functional disorders. It has been shown to be the most sensitive and most specific test for this discrimination; clearly outperforming blood tests such as CRP or ESR. Faecal calprotectin correlates with disease activity and is able to predict relapses in IBD. This makes faecal calprotectin useful for both diagnosis and monitoring of IBD patients.
