NEONATAL HYPER BILURUBINEMIA

BILIRUBIN
n Non-polar, water insoluble compound requiring conjugation with glucuronic acid to form a water soluble product that can be excreted.
n It circulates to the liver reversibly bound to albumin



BILIRUBIN PHYSIOLOGY
n Increased production in neonate due to larger red cell volume, which produces bilirubin as cells are broken down and shorter RBC life span, so broken down faster.
n Heme is catabolized within the reticuloendothelial system by heme oxygenase to form biliverdin.
n Biliverdin is metabolized to bilirubin in the presence of biliverdin reductase


n Ligandins responsible for transport from plasma membrane to endoplasmic reticulum.
n Bilirubin conjugated in presence of UDPGT (uridine diphosphate glucuronyl transferase) to mono and diglucoronides, which are then excreted into bile canaliculi.

Enterohepatic Circulation
n Meconium contains 100-200mg of conjugated bilirubin at birth.
n Conjugated bilirubin is unstable and easily hydrolyzed to unconjugated bilirubin.
n This process occurs non-enzymatically in the duodenum and jejunum and also occurs in the presence of beta-glucuronidase, an enteric mucosal enzyme, which is found in high concentration in newborn infants and in human milk.


Conjugation
n Since conjugated bilirubin crosses the placenta very little, conjugation is not active in the fetus with levels of UDPGT about 1% of adult levels at 30 - 40 weeks gestation
n After birth, the levels of UDPGT rise rapidly but do not reach adult levels until 4-6 weeks of age.
n Ligandins, which are necessary for intracellular transport of bilirubin, are also low at birth and reach adult levels by 3-5 days.


CONJUGATED VS UNCONJUNCATED HYPERBILI
n Conjugated hyperbilirubinemia is always pathologic
n When the total bili is quite high, the conjugated fraction can rise to as high as 20% of the total, although it usually stays under 1.0.
n Always check a total and direct, so that you can be sure you are excluding conjugated hyperbilirubinemia, which has totally different etiologies and treatments.


KERNICTERUS
n Why we care about indirect hyperbilirubinemia
n Staining of the brain by bilirubin
n Early symptoms-acute bilirubin encephalopathy-poor feeding, abnormal cry, hypotonia,
n Intermediate phase-stupor, irritability, hypertonia
n Late – shrill cry, no feeding, opisthotonus, apnea, seizures, coma, death

n Late sequelae can include
gaze abnormalities
feeding difficulties
dystonia
incoordination
choreoathetosis
sensorineural hearing loss
painful muscle spasms

n Incidence of bilirubin levels>30 1/10,000
n Over 120 cases kernicterus documented since 1990
n Overwhelming majority term, breastfed
n Majority of those had levels in high 30s to 40s.
n Lowest level recorded in case series of 111 from 1991-2002 was 20.7, but the mean was 38.
n Many cases had no planned follow up and had been discharged early (<48 hours).


KERNICTERUS AND FREE BILIRUBIN

n An article published this year in Pediatrics makes the case for establishing free bilirubin levels rather than total serum bilirubin levels to monitor jaundice and assess risk for kernicterus
n Since bilirubin travels bound to albumin predominantly, the free bilirubin is inversely proportional to the albumin concentration.

ALBUMIN
n A low albumin level could possibly be the reason behind kernicterus occurring in some infants at relatively low bilirubin levels.
n There was a report of a 29 week infant whose peak bilirubin level was only 15.7 and yet developed classic kernicterus with spasticity, dystonia, ballismus, and gaze abnormalities.
n Her bilirubin/albumin molar ratio was 0.67. It has been suggested that a ratio of >0.5 might be a threshold in sick preterm infants.

n Wenneberg et. al. suggest that an infant with an albumin level of 2 would be at the same risk for kernicterus with a bilirubin of 15 as an infant with a bilirubin of 30 and an albumin level of 4.
n We do not have data on albumin levels in healthy term infants, but most likely, hypoalbuminemia is a concern in extremely preterm or otherwise sick infants.

RISK FACTORS FOR SIGNIFICANT JAUNDICE
n Gestational Age
n Race
n Family history of jaundice requiring phototherapy
n Hemolysis (ABO or other)
n Severe bruising
n Breastfeeding

TIME COURSE OF JAUNDICE
n Pathologic by definition if significant in first 24 hours
n Usually begins to peak by 48 hours and continues until 96 hours
n In Asian infants and preterm infants, peak can continue out to 5-7 days.

RISK FACTORS-RACE
n Asians-highest risk
Levels peak at 16-18 as opposed to average Caucasian levels of 6-8. There is also a later peak which can occur at 5-7 days.

n Black infants have a lower peak, rarely exceeding 12. (but they have a much higher incidence of G6PD deficiency)

n Caucasians are in the middle.

RISK FACTORS-GESTATIONAL AGE
n The younger the gestation, the higher the risk of jaundice.
n 37 weeks more prone to jaundice than 40 weeker who is more prone than a 42 weeker.
n 35 and below is much more prone
n Extreme preemies also more prone to kernicterus and are treated at much lower levels.

RISK FACTORS-FAMILY HX
n A child whose sibling needed phototherapy is 12 times more likely to also have significant jaundice.

n Frequently peak bilirubin levels correlate between siblings.

RISK FACTORS-HEMOLYSIS
n ABO Incompatibility is the most common cause of hemolysis causing jaundice.
n Only 10-20% of infants with ABO mismatch develop significant jaundice.
n Some of these infants, however, develop very significant jaundice quickly.
n Coombs positive ABO is more likely to cause hemolysis, but many babies will be asymptomatic. Conversely, Coombs negative ABO mismatch does occasionally cause significant hemolysis, but this is rather rare.

RISK FACTORS-PATHOLOGIC
n G6PD Deficiency
n Hereditary Spherocytosis
n Glucuronyl Transferase Deficiency Type 1 (Crigler Najar Syndrome)
n GT deficiency Type 2 (Arias Syndrome)
n Polycythemia


BREASTMILK/BREASTFEEDING JAUNDICE
n Breastfeeding jaundice occurs early
n It is due to the lack of breast milk
n It is often associated with poor passage of meconium.
n Treatment should be aimed at supporting breastfeeding while supplementing as needed to avoid extreme weight loss, dehydration, and worsening jaundice.

n Breast milk jaundice is a different, more benign entity, which tends to occur late in the first week or afterwards.
n It is actually due to something in the breast milk which tends to prolong jaundice.
n Usually weight gain is good, and the baby is otherwise well.
n Jaundice might persist as late as 3-4 weeks, but usually will peak by 2 weeks.
n Textbook treatment is to interrupt breastfeeding (I usually do not do this).

ASSESSING THE RISK OF JAUNDICE BY THE NUMBERS

n Maisels’ and Kring’s study showed that not all early higher TcB will continue going up.
n They divided the rate of rise to be concerned with into
n 6-24hr >0.22/hr
n 24-48 >0.15/hr
n 48+ >0.06/hr

THERAPIES-PHOTOTHERAPY
n Phototherapy has been the mainstay of treating hyperbilirubinemia since the 1960s.
n Phototherapy causes structural isomerization, forming lumirubin, which is then excreted in the bile and urine.
n Since photoisomers are water soluble, they should not be able to cross the blood-brain barrier, so starting phototherapy should decrease the risk of kernicterus by turning 20-25% of bilirubin into a form unable to cross, even before the level has lowered significantly.


n Bilirubin absorbs light best at 450 nm, but longer wavelenths penetrate skin better.
n Make sure skin is as exposed as possible and that light is not too far from baby.
n Fiberoptic light (bili blanket) is much less efficacious on its own.


THERAPIES-EXCHANGE TRANSFUSION
n Double volume exchange transfusion was a common procedure prior to advent of Rhogam and phototherapy.
n Now fortunately a rare occurrence
n Used for bilirubin >25 in a term infant and not decreasing despite phototherapy