Total bilirubin, indirect bilirubin and direct bilirubin are one of the biochemical indicators, and total bilirubin is the sum of indirect bilirubin and direct bilirubin. The source of indirect bilirubin in human body is mainly hemoglobin released from the decomposition of aging red blood cells, which is fat-soluble bilirubin and cannot be dissolved in water or excreted from urine, but can only enter the intestine and be eliminated from the body in the form of bile. Direct bilirubin, also known as conjugated bilirubin, is formed when indirect bilirubin is transported to the liver and combined with glucuronic acid. Direct bilirubin is a water-soluble bilirubin that is soluble in water and can be excreted in the urine. The shade of yellow color in urine is mainly determined by the concentration of direct bilirubin in the urine.