Calprotectin. Molecular model showing the secondary structure of calprotectin. This protein is found in large quantities in neutrophils, a type of white blood cell involved in inflammatory response. Tests for calprotectin in faecal samples can distinguish between inflammatory bowel diseases (IBDs), such as Crohn's disease, some cancers and ulcerative colitis, where calprotectin levels are raised, and irritable bowel syndrome (IBS), where calprotectin levels are normal. IBDs need further investigation with invasive tests, while IBS doesn't. Measurement of faecal calprotectin levels can also be used to determine if treatments for IBDs are working.