Bilirubin (TCB) is a product of the breakdown and destruction of senescent red blood cells in the circulation in the monocyte-phagocyte system of the liver, spleen, and bone marrow. Total bilirubin (TB) includes both indirect bilirubin (IB) and direct bilirubin (DB) forms. Unconjugated bilirubin is a metabolic product of hemoglobin, which is taken up by hepatocytes and excreted from the bile duct by combining with glucuronic acid to form water-soluble bilirubin. Problems in any one of these can cause jaundice, which mainly manifests itself as yellow staining of the skin and sclera. A normal bilirubin value does not exactly parallel the health of the liver, and the assessment of liver function should be determined by interpreting the patient’s symptoms and other materials together. Serum bilirubin helps to detect jaundice that is not yet observable to the naked eye and often responds to hepatocellular damage or biliary stasis. Positive urinary bilirubin also indicates an increase in blood-conjugated bilirubin, which can be increased by urinary excretion when the liver is unable to process the urobilinogen absorbed by the intestine. Therefore, the bilirubin value in the serum has a reference value for whether the liver is abnormal or not. When liver damage or reduced liver function is determined, a regular hospital should be visited to look for various causative factors, followed by examination and treatment.