- Jaundice: a yellow or green/yellow hue to the skin, sclerae, and mucous membranes which can be appreciated at serum bilirubin levels >2 mg/dL. Intensity of color is directly related to the serum bilirubin level.
- Unconjugated bilirubin: 80% is due to hemoglobin turnover and 20% is from degradation of hepatic and renal heme proteins. It is a hydrophobic compound that must be carried to the liver by albumin for processing.
- Conjugated bilirubin: conjugated to glucuronic acid in the liver, a water-soluble derivative that helps lipid emulsification and absorption
- Direct bilirubin: conjugated bilirubin plus bilirubin that is covalently bound to albumin (delta fraction)
- Direct bilirubin is higher than a measured conjugated bilirubin and has a longer half-life.
- Conjugated hyperbilirubinemia (direct hyperbilirubinemia): a conjugated bilirubin of >2 mg/dL or >20% of the total bilirubin
The most common causes of pathologic jaundice are as follows:
- Newborn period: biliary atresia, idiopathic neonatal hepatitis, α1-antitrypsin deficiency, infection
- Older child: autoimmune hepatitis, viral hepatitis, Wilson disease, biliary obstruction
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