Jaundice visible to the naked eye can occur in neonates with blood bilirubin above 5-7 mg/dl (adults above 2 mg/d1). Some cases of high unconjugated bilirubin (indirect bilirubin as indicated by the test report) may cause bilirubin encephalopathy (nuclear jaundice), with a high mortality rate in severe cases and sequelae in survivors. Physiological jaundice (physiologicaljaundice) is due to the characteristics of neonatal bilirubin metabolism, about 50% to 60% of term infants and 80% of premature infants appear physiological jaundice, which is characterized by: ① good general condition; ② full-term infants jaundice 2-3 days after birth, 4-5 days to reach the peak, 5-7 days to subside, no later than 2 weeks; premature infants jaundice more in the postnatal 3 to 5 days after birth, peaking at 5 to 7 days and receding at 7 to 9 days, with a maximum delay of 4 weeks; ③ daily serum bilirubin elevation <85umol/L (5mg/d1); ④ serum bilirubin <221/umol/L (12.9mg/d1) in term infants and <257umol/L (15mg/d1) in preterm infants. Pathologic jaundice: ① jaundice within 24 hours after birth; ② serum bilirubin >22lumol/L (12.9mg/d1) in term infants, >257umol/L (15mg/d1) in preterm infants, or a daily rise of more than 85umol/L (5mg/d1); ③ duration of jaundice >2 weeks in term infants, >4 weeks in preterm infants; ④ jaundice recedes and returns; ⑤ serum conjugated bilirubin > 34umol/L (2mg/d1). With any one of them can be diagnosed as pathological jaundice. Pathological jaundice arises from a variety of causes, and clinical disease is often dominated by a particular cause, which can be divided into three categories for ease of description: 1, excessive bilirubin production. 2, low hepatic uptake and/or conjugated bilirubin function. 3, impaired bile excretion.