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Understanding Pediatrics: Hyperbilirubinemia

Normal neonatal bilirubin levels:

  • Total bilirubin (neonates):
    • Conjugated bilirubin: 0-10 μmol/L
    • Total bilirubin: 1.7-180 μmol/L
  • The bilirubin value at which you need to initiate phototherapy or exchange therapy however depends on number of hours since birth as well as accompanying risk factors
  • We get concerned when the percentage of conjugated bilirubin is greater than 10 percent of the total bilirubin since conjugated bilirubin is ALWAYS pathological

Conjugated vs Unconjugated bilirubin

  • Quick recap of lifecycle of bilirubin
    • Blood cells break down releasing heme products that eventually become converted to unconjugated bilirubin (indirect bilirubin)
    • Unconjugated bilirubin is not water soluble and is therefore bound to albumin in the bloodstream
    • Liver removes unconjugated bilirubin from bloodstream by conjugating it with glucuronate which makes it water soluble
    • From there it may be excreted into the gut as one of the components of bile
    • Bacteria in the intestine convert conjugated bilirubin into urobilinogen which then gets converted into stercobilinogen and then finally stercobilin
    • Stercobilin is the component of stool that makes it brown
    • Some of the urobilinogen gets reabsorbed and filtered into the urine where it gets converted into urobilin which makes the urine yellow

Stercobilin makes stool brown! Urobilin makes urine yellow! Both are derived from bilirubin which comes from heme.

  • Conjugated hyperbilirubinemia
    • Always pathological
    • Because it is water soluble it cannot pass the blood brain barrier and therefore cannot cause kernicterus (brain dysfunction caused by high bilirubin)
    • Because it is water soluble it can be excreted from the body via the urine, making it dark
    • Pathologic jaundice involves a faster rate of bilirubin increase and a higher peak
    • Presents within the first 24 hours of life
    • Takes longer than 1-2 weeks (1 week term, 2 week preterm)
  • Unconjugated hyperbilirubinemia
    • Usually physiological, sometimes pathological
    • Not water soluble, can cross blood brain barrier and cause kernicterus
    • Because it is not water soluble it cannot pass into the urine and will not affect urine colour
    • Physiologic jaundice involves a slower rate of bilirubin increase and a lower peak
    • Presents after the first 24 hours of life
    • Resolves in 1-2 weeks

Phototherapy and Exchange transfusions

Phototherapy involves the use of blue light to accelerate the conversion of unconjugated bilirubin to conjugated bilirubin.

You can see why it makes sense that phototherapy should only be used in cases of physiologic or unconjugated hyperbilirubinemia.

Exchange transfusions should only be if the neonate’s bilirubin levels are so high that they pass the threshold for their age and risk factors

Approach to a yellow baby

  • Check conjugated, unconjugated and total bilirubin levels
  • If conjugated, there is underlying pathology and you can perform liver U/S and liver biopsy to confirm
    • Impaired transportation of conjugated bilirubin
      • Dubin-Johnson syndrome
      • Rotor syndrome
    • Obstruction of biliary tree
      • Biliary cyst
      • Biliary atresia – lack of extrahepatic biliary duct including the common bile duct
      • Alagille syndrome – intrahepatic biliary duct hypoplasia
  • If unconjugated bilirubin is elevated then it is most likely physiologic
    • First step is to perform if not already done, blood typing of the mother and infant to assess for ABO or Rh incompatibility and a Coombs test
    • If Coombs test is positive then the elevated bilirubin is due to isoimmunization
    • If Coombs test is negative but
      • Hemoglobin low, then hyperbilirubinemia is due to cephalohematoma
      • Hemoglobin high, then hyperbilirubinemia is due to twin-twin transfusion or delayed cord clamping
    • If the hemoglobin is low/normal, check reticulocyte count
      • If reticulocyte count is high, then this is due to hemolysis
        • Hemolysis from ABO or Rh incompatibility
        • Hemolysis from sickle cell anemia
        • Hemolysis from thalessemia
        • Hemolysis from G6PD deficiency
          • Glucose-6-phosphate dehydrogenase (G6PD) deficiency leads to impaired production of reduced glutathione which is necessary to protect RBCs from oxidative stress
          • It can separately lead to jaundice without anemia through decreased conjugation of bilirubin
      • If reticulocyte count is normal, then this is due to
        • Breast milk jaundice (quality issue) – factors in breast milk that inhibit conjugation
        • Poor feeding (quantity issue) – decreased bowel function due to poor feeding results in increased reabsorption of bilirubin from the GI tract into the enterohepatic circulation
        • Rarely it can also be due to diseases that cause impaired conjugation of bilirubin
          • Gilbert syndrome
          • Crigler-Najjar syndrome

How to present a bilibaby concisely

This is baby boy seen on day X of life. Risk factors include x, y z. Their birth weight was blank. They were discharged on blank with a discharge weight of blank. Today their weight is blank representing an increase/decrease from weight checked 2 days ago and their bilirubin today is blank. Physical exam was unremarkable. Based on bilirubin and weight gain, they can be discharged from the bilirubin clinic.