Calprotectin is a protein produced by polymorphonuclear neutrophils, monocytes, and squamous epithelium (except for skin epithelium). Calprotectin is excreted in large quantities in the feces when the intestinal mucosa is damaged and is a marker of leukocyte activity and inflammation in the gastrointestinal tract. Fecal calprotectin levels directly correlate with the number of neutrophils in the intestinal lumen.