Blood bilirubin, also known as total serum bilirubin, has a normal range of 3.7-17.1 umol/L. Total bilirubin consists of two components, one being direct bilirubin and the other being indirect bilirubin. By measuring the concentration of total bilirubin, it is possible to make a clear diagnosis of the presence of jaundice. In general, jaundice visible to the naked eye occurs when the serum total bilirubin concentration exceeds 34umol/L. If it is lower than 34umol/L, no obvious jaundice visible to the naked eye usually occurs, and this condition is called occult jaundice. By measuring the concentration of direct and indirect bilirubin, it is also possible to make a general determination of the type of jaundice. In a patient with jaundice, an increase in total serum bilirubin, but mainly an increase in indirect bilirubin concentration, is most often caused by hemolytic anemia, in which the destruction of red blood cells by lysis exceeds the processing function of the liver, resulting in an abnormal increase in unconjugated bilirubin, or indirect bilirubin.