The normal reference value of total bilirubin is 5.13～22.24 mol/L (0.3～1.3㎎/dl). The exact value may be adjusted depending on the test method, etc., and is based on the reference value of the local hospital. Total bilirubin is the sum of direct bilirubin and indirect bilirubin. Indirect bilirubin, also called unconjugated bilirubin, is bilirubin that is not conjugated to glucuronic acid, is insoluble in water, and cannot be excreted in urine through the kidneys. Direct bilirubin, also called conjugated bilirubin, is formed when indirect bilirubin binds to glucuronic acid in liver cells, is soluble in water, and can be excreted in the urine through the kidneys. The liver plays a very important role in the metabolism of bilirubin, including the uptake, binding and excretion of indirect bilirubin in the blood by hepatocytes, and any one of these processes can cause bilirubin to accumulate in the blood, resulting in jaundice, such as yellowing of the sclera and itching of the skin. Determination of serum total bilirubin is an important test item in liver and biliary function examination, which can accurately reflect the degree of jaundice and is of great significance in clinical diagnosis of hidden jaundice.