Urobilinogen is the result of aging red blood cells being destroyed in the liver or spleen, and the release of heme from the red blood cells, unbound to protein, called unconjugated bilirubin, which is discharged into the intestinal cavity through the bile duct, where it is broken down by bacteria in the intestine and turned into urobilinogen. Generally most of the urobilinogen is excreted with feces, and a small portion is absorbed by the intestinal wall back to the liver, then from the liver into the kidneys and blood, forming the hepatic-intestinal circulation of bilirubin, which becomes urobilin after being excreted with urine. Urobilirubin is conjugated bilirubin, due to its small molecular weight and high solubility, it can be filtered through the glomerulus and excreted from the urinary system, that is, urobilirubin, urobilinogen and urobilin will form urinary triple bile.