Calprotectin is a protein produced by neutrophils, the white blood cells responsible for defending the body against “attacks.” When inflammation occurs in the digestive tract, neutrophils secrete large amounts of calprotectin, which ends up in the stool.
Calprotectin levels above 150 milligrams per kilogram (mg/kg) of stool indicate that an inflammatory process is occurring in the digestive tract (Crohn’s disease, ulcerative colitis, etc.) but they do not specify its location or cause. The higher the calprotectin levels, the more severe the inflammation. High calprotectin levels can also signal a bacterial or parasitic intestinal infection or cancer. High calprotectin levels must be confirmed by colonoscopy to determine the cause of inflammation.
Calprotectin levels below 50 mg/kg indicate that the intestinal symptoms are probably due to a more benign bowel condition such as irritable bowel syndrome or a viral infection, thus avoiding the need for colonoscopy in most cases.
Intermediate levels of calprotectin (between 50 and 150 mg/kg) are in a grey area, meaning they do not assist in establishing precise clinical management, and the test must be repeated on a new sample. A colonoscopy is indicated if the second test shows a calprotectin level above 50 mg/kg.