Total bilirubin is a general term for direct and indirect bilirubin, and in clinical examination, there are two indicators: total serum bilirubin and total urinary bilirubin. The normal range of serum total bilirubin in newborns varies with the number of days of birth, while the reference range of serum total bilirubin in adults is relatively fixed and usually ranges from 3.4 to 17.1 μmol/L. If it is in the range of 34.0 to 171.0 μmol/L, it indicates a serious elevation of bilirubin. The normal value of urinary total bilirubin is about 3.4μmol/L, and it is seriously elevated when the concentration exceeds 34.0μmol/L. 1. Serum total bilirubin: When serum total bilirubin is seriously elevated, it may be due to biliary obstructive disease or liver disease that causes massive damage to liver cells, resulting in a significant increase of bilirubin into the blood. Hemolytic diseases lead to the destruction of red blood cells, causing an increase in indirect bilirubin, which can also cause a serious increase in total serum bilirubin when blood is drawn; 2. Urinary total bilirubin: Usually, as serum bilirubin increases, urinary bilirubin will also increase. However, hemolytic diseases are less likely to cause elevated urinary total bilirubin, mainly because indirect bilirubin is easily combined with protein and thus does not easily enter the urine, so the urinary total bilirubin can exclude whether it is a hemolytic disease. The level of total serum bilirubin is also sometimes indicative of the severity of jaundice. Serum total bilirubin in the range of 17.2-34.2 μmol/L is called occult jaundice and can have no clinical manifestations. Mild jaundice has a total bilirubin range of 34.2-171 μmol/L and may have mild scleral yellowing; moderate jaundice is defined as a total bilirubin of 171-342 μmol/L, while greater than 342 μmol/L is considered severe jaundice.