S100A9 and inflammatory bowel disease: Fecal calprotectin (S100A8/S100A9 heterodimer) is used as a highly sensitive and non-invasive marker for tracking intestinal inflammation and distinguishing between IBD and irritable bowel syndrome (IBS), while fecal S100A12 is granulocyte-specific and thus more reliable for the clinical detection of bacterial gastroenteritis compared to calprotectin [12,13].