Patient's question:
How much total bilirubin does a general child have within 2 weeks?Doctor's answer:
Hello, neonatal jaundice (eojataljaudice) is caused by the accumulation of bilirubin (mostly unconjugated bilirubin) in the body. Its causes are complex, including both physiological and pathological factors. Some pathological jaundice can lead to central nervous system damage, resulting in bilirubin encephalopathy. Therefore, it is essential to strengthen clinical observation of neonatal jaundice, identify the cause as soon as possible, and provide timely treatment.[Characteristics of Bilirubin Metabolism in Newborns]
(1) Increased Bilirubin Production
Newborns generate approximately 8.8 mg/kg of bilirubin daily, while adults produce only 3.8 mg/kg. The reasons are as follows:
- Fetal oxygen partial pressure is low, leading to the production of a higher number of red blood cells. After birth, the oxygen partial pressure increases, resulting in relatively excessive red blood cells and their destruction.
- The half-life of fetal hemoglobin is short, and newborn red blood cells have a shorter lifespan (20–40 days shorter than adults), shortening the cycle of bilirubin formation.
- Other sources of bilirubin production are higher, such as heme protein from organs like the liver (e.g., catalase, cytochrome P450) and precursors of bilirubin from ineffective hematopoiesis in the bone marrow (a small amount of red blood cells are destroyed during their maturation).
(2) Insufficient Transport Capacity for Bilirubin
Newborns often have varying degrees of acidosis after birth, which affects the binding of bilirubin to albumin in the blood. Preterm infants have lower albumin levels than full-term infants, both of which result in insufficient transport capacity for bilirubin.
(3) Immature Liver Function
① The content of Y and Z proteins, which are essential for bilirubin uptake by liver cells in newborns, is low and takes 5–10 days to reach adult levels.
② The ability to form conjugated bilirubin is poor, as the content and activity of uridine diphosphate glucuronosyltransferase (UDPGT) in liver cells are low (only 0–30% of normal levels). This enzyme cannot effectively conjugate lipid-soluble unconjugated bilirubin (indirect bilirubin) with glucuronic acid to form water-soluble conjugated bilirubin (direct bilirubin). The activity of this enzyme gradually returns to normal after one week.
③ The ability to excrete conjugated bilirubin is poor, making it prone to bile stasis.
(4) Characteristics of Enterohepatic Circulation
Newborn infants have a low number of intestinal bacteria, which cannot reduce bilirubin in the intestines to stercobilinogen or urobilinogen. Additionally, the activity of glucuronidase in the intestinal lumen is high, hydrolyzing conjugated bilirubin into glucuronic acid and unconjugated bilirubin, which is then reabsorbed by the intestine and reaches the liver via the portal vein. Due to these characteristics, newborns' ability to absorb, conjugate, and excrete bilirubin is only 1–2% of that of adults, making them highly susceptible to jaundice. This is especially true when newborns are in states such as hunger, hypoxia, delayed meconium passage, dehydration, acidosis, cranial hematoma, or intracranial hemorrhage, which exacerbate jaundice.
[Classification of Neonatal Jaundice]
(1) Physiological Jaundice
Due to the characteristics of bilirubin metabolism in newborns, approximately 50–60% of full-term infants and >80% of preterm infants develop jaundice within 2–3 days after birth, peaking at 4–5 days. General condition is good, with jaundice usually resolving within 2 weeks in full-term infants and extending to 3–4 weeks in preterm infants.
Current upper limits for serum bilirubin levels for physiological jaundice, previously used in clinical practice, have been questioned. For full-term infants, the limit was <205.2 μmol/L (12 mg/dL), and for preterm infants, <257 μmol/L (15 mg/dL). However, smaller preterm infants may develop bilirubin encephalopathy even if bilirubin levels are <171 μmol/L (10 mg/dL). International guidelines now set the threshold for physiological jaundice in full-term infants at <220.59 μmol/L (12.9 mg/dL). Domestic scholars have found that the upper limit of bilirubin levels for physiological jaundice in normal full-term infants ranges from 205.2 to 256.5 μmol/L (12–15 mg/dL), with 31.3–48.5% exceeding the original 205.2 μmol/L. Similarly, 42.9% of preterm infants have serum bilirubin levels exceeding 256.2 μmol/L. Therefore, nationwide collaborative research is being conducted to revise the diagnostic criteria for physiological jaundice in China.
(2) Pathological Jaundice
Pathological jaundice often exhibits the following characteristics:
① Jaundice appears within 24 hours after birth.
② Severe jaundice, with serum bilirubin levels >205.2–256.5 μmol/L or rising by >85 μmol/L (5 mg/dL) daily.
③ Prolonged jaundice duration (full-term infants >2 weeks, preterm infants >4 weeks).
④ Jaundice that resolves and then reappears.
⑤ Serum conjugated bilirubin >26 μmol/L (1.5 mg/dL).
Active investigation of the cause is necessary for pathological jaundice. The main causes include:
1. Infectious
(1) Neonatal hepatitis: Most cases are caused by viral infections in utero, with cytomegalovirus being the most common. Others include hepatitis B, rubella, herpes simplex, coxsackie virus, EB virus, listeria, syphilis, and toxoplasma. Infection can be transmitted through the placenta or during delivery. Jaundice typically appears 1–3 weeks or later after birth. In severe cases, feces may appear pale or grayish-white, urine may be dark yellow, and symptoms may include anorexia, vomiting, and mild-to-moderate hepatomegaly.
(2) Neonatal sepsis.
2. Non-infectious
(1) Neonatal hemolytic disease.
(2) Biliary atresia: This condition is now confirmed to be mostly caused by intrauterine viral infections leading to postnatal progressive cholangitis, biliary fibrosis, and biliary atresia. If the bile duct wall is weak, it may develop into a bile duct cyst. Jaundice typically appears 2 weeks after birth and worsens progressively. Feces change from pale yellow to white, the liver progressively enlarges with a hard, smooth edge, and liver function changes primarily involve increased conjugated bilirubin. It may gradually progress to cirrhosis after 3 months.
(3) Breast milk jaundice: Approximately 1% of breastfed infants develop breast milk jaundice, characterized by increased unconjugated bilirubin without hemolysis. It often overlaps with physiological jaundice and persists without resolution, with serum bilirubin levels reaching as high as 342 μmol/L (20 mg/dL). Infants are generally well, and jaundice typically decreases after 4–12 weeks. No other causes of jaundice are identified. If jaundice decreases by 3 days after stopping breastfeeding, the diagnosis is confirmed. Current theories suggest that high β-glucuronidase activity in this type of breast milk increases the reabsorption of bilirubin in the intestines, leading to jaundice. Some researchers propose that the cause is a lack of bacteria in the intestines of breastfed infants that can convert bilirubin to urobilinogen and stercobilinogen.
(4) Hereditary diseases: G6PD deficiency is common in southern China, with a higher incidence of kernicterus. Other conditions include pyruvate kinase deficiency, spherocytosis, galactosemia, α1-antitrypsin deficiency, and cystic fibrosis.
(5) Drug-induced jaundice: Such as that caused by vitamin K3, K4, or neomycin.