Bilirubin Transport and Neurotoxicity

Introduction to Bilirubin Transport

Bilirubin is transported in plasma bound to albumin, and the unbound or "free" bilirubin can cross the blood-brain barrier and cause neuronal damage, with albumin binding capacity reduced in sick and premature infants, increasing risk 1
The bilirubin/albumin (B/A) ratio can be used as a surrogate marker for free bilirubin 1

Predischarge bilirubin measurement and plotting on hour-specific nomogram is recommended for all newborns, with risk assessment necessary before discharge 1
Risk assessment factors for hyperbilirubinemia include family history of neonatal jaundice, gestational age (preterm infants at higher risk), exclusive breastfeeding, and presence of hemolysis, as recommended by the American Academy of Family Physicians and the American Academy of Pediatrics 1, 2

G6PD deficiency occurs in 11-13% of African Americans and was implicated in 31.5% of kernicterus cases in one report 1
Exchange transfusion carries risks including hypoxic-ischemic encephalopathy and complications from blood products 1
Phototherapy is effective for indirect hyperbilirubinemia but not for direct hyperbilirubinemia, according to the American Academy of Pediatrics 1
The following conditions and their characteristics can aid in diagnosis:

Condition	Characteristic	Treatment
Biliary obstruction	Elevated direct bilirubin, suspected dominant stricture	Evaluate with MR cholangiography or endoscopic retrograde cholangiography, consider endoscopic or surgical intervention
Physiologic jaundice	Elevated indirect bilirubin, no underlying disease	Monitoring and supportive care
Pathologic jaundice	Elevated direct bilirubin, underlying disease	Treatment of underlying disease

A direct bilirubin level >1.0 mg/dL when total bilirubin is ≤5 mg/dL is considered abnormal in infants, and bilirubin levels should be interpreted according to the infant's age in hours, as recommended by the American Academy of Pediatrics 1

Phototherapy should be initiated when total serum bilirubin (TSB) reaches thresholds based on age of infant in hours, gestational age, and presence of risk factors, using the American Academy of Pediatrics (AAP) phototherapy nomogram 3, 1
Intensive phototherapy should use special blue fluorescent tubes or LED light sources with output in the blue-green spectrum (425-475 nm) and an irradiance level of >30 mW/cm² per nm, as recommended by the American Academy of Pediatrics (AAP) 1
Total serum bilirubin (TSB) measurements should be continued until bilirubin levels are clearly declining, and IVIG (0.5-1 g/kg over 2 hours) should be considered if TSB is rising despite intensive phototherapy, as suggested by the AAP 1
Exchange transfusion should be prepared for if TSB ≥25 mg/dL (428 μmol/L), or if TSB reaches exchange level per AAP guidelines, as recommended by the AAP 1

Successful breastfeeding should be supported by advising mothers to nurse 8-12 times per day for the first several days, and avoid routine supplementation with water or dextrose water in nondehydrated breastfed infants, as suggested by the American Academy of Pediatrics 1
Breastfeeding can be continued during phototherapy, although breastfed infants may have higher bilirubin levels than formula-fed infants due to physiologic reasons, as stated by the AAP 1, 4
Ensuring adequate intake by monitoring weight gain pattern, 4-6 thoroughly wet diapers in 24 hours, and 3-4 stools per day with appropriate yellow color in breastfed infants is recommended by the American Academy of Pediatrics 1

Follow-up should be scheduled at 2-4 weeks to check hemoglobin levels, especially with rare antibodies, to monitor for late-onset anemia, as recommended by the AAP 1
Regular monitoring of bilirubin levels and liver function tests is necessary until the condition is resolved, with the frequency depending on the severity of elevation and underlying cause, as recommended by 5, 6
Newborns with severe hyperbilirubinemia are at risk of bilirubin encephalopathy, which can occur as early as the first 24 hours of life, with the highest risk during the first week of life when bilirubin levels typically peak, especially in those with gestational age <38 weeks, exclusive breastfeeding, jaundice in the first 24 hours of life, hemolytic conditions, previous sibling with severe jaundice, cephalohematoma or significant bruising, or East Asian, Mediterranean, or Native American ethnicity 1
The incidence of chronic bilirubin encephalopathy is estimated at 0.9 per 100,000 live births, according to the American Academy of Family Physicians 2