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Bilirubin Metabolism in the Newborn


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What are 3 pathologic causes of jaundice in newborns?
(1) Increased enterohepatic circulation of bilirubin, (2) Impaired ability to conjugate bilirubin, (3) Deficiency in hepatic uptake of bilirubin.
What are 4 pathological causes of increased bilirubin production in newborns?
(1) Idiopathic ethnic differences, (2). blood group incompatibilities, (3) enzyme deficiencies, (4) structural deficits in RBC.
What are 3 physiological causes of hyperbilirubinemia in newborns?
(1) High RBC turnover + high RBC mass, (2) Limited ability to conjugate bilirubin, (3) increased enteroheptic circulation
What happens in Gibert's syndrome?
Hyperbilirubinemia due to deficient hepatic uptake of bilirubin
What does a deficiency uridine diphosphate glucoronosyltransferase cause? Is this common?
(a) a deficiency in this enzyme results in the decreased ability to conjugate bilirubin, (b) yes, it is an important cause of neonatal jaundice.
What is crigler-Najjar Syndrome type I? What are the clinical features?
(a) It is severe deficiency uridine diphosphate glucoronosyltransferase, (b) bilirubin encephalopathy in the first few days or month of life.
What is crigler-Najjar Syndrome type II? What are the clinical features?
(a) not as severe a uridine diphosphate glucoronosyltransferase as with type II, below 20 mg/dl, (b) bilirubin encepahlaopathy is rare.
What does a deficiency in G6P result in?
Increased risk of hemolysis
What is the major clinical feature (concern) of hyperbilirubinemia?
(1) neurotoxic effects.
What are the 4 ways cells are damaged by hyperbilirubinemia? (hint: 1ab and 2
BR inhibits mitochondrial enzymes that (1) interfere with DNA synthesis, (2) induce DNA-strand breakage, (3) inhibit protein synthesis and phosphorylation
At what day do full term babies' bilirubin levels peak?
3-5 days
At what day do preterm babies' bilirubin levels peak?
5-7 days
Which babies have a greater likelihood of having elevated (above 12 mg/dl) bilirubin levels, formula or breast fed?
breast fed
What are 5 transitional causes (from fetus to neonate) causes for hyperbilirubinemia?
(1) the fetus transferred all its bilirubin through the placenta, (2) neonates have low levels of ligandin (involved in bili transport and storage), (3) neonate have decrased levels of glucuronyl transferase (conjugates BR), (4) at birth they have elevated levels of ß-gluconidase, (5) absence of gut bacteria which convert the BR into uncongugated
What are the 6 criteria that rule out physiologic jaundice?
(1) clincal jaundice with the first 24 hours, (2) TSB increasing by 5mg/dl/day, (3) TSB > 12.9/dl in full term babies, (4) TSB> 15mg/dl in preterm babies, (5) Direct serum bilirubin > 1.5mg/dl, (6) clinical jaundice after 1 week for full term and 2 weeks for preterm
What 6 things can account for increased RBC destruction associated with hyperbilirubinemia?
(1) isoimmunization (ABO incompatibility⬦ mom's Ab), (2) RBC biochemical defects, (3) RBC structural abnormalities, (4) infection, (5) sequestered/extravasated blood (bruising), (6) swallowed blood
What 5 things can account for increased enterohepatic circulation associated with hyperbilirubinemia?
(1) intestinal obstruction, (2) pyloric stenosis, (3) meconium ileus (intestinal obstruction associated with cystic fibrosis of the pancreas), (4) paralytic ileus (Nonmechanical obstruction of the bowel from paralysis of the bowel wall), (5) a congenital absence of nerves in the smooth muscle wall of the colon that results in buildup of feces.
What does Crigler-Najjar type II respond to?
What are the 4 neonatal hyperbilirubinemia inherited disorders?
(1&2) Crigler-Najjar type I & II, (3) Gilbert's disease, (4) Lucey-Driscoll syndrome (transient)
Since direct (conjugated) hyperbilirubinemia is rarely seen in neonates (and is always pathologic), what two other reasons that direct (conjugated) hyperbilirubinemia arises?
(1) hepatic dysfunction, (2) disturbances in ductal function of the liver.
With respect to neonatal (conjugated) hyperbilirubinuria, what are the two causes of hepatocellular dysfunction?
(1) hepatitis ( infectious and noninfectious), (2) metabolic disorders
With respect to neonatal (conjugated) hyperbilirubinuria, what are 3 causes of ductal dysfunction?
(1) biliary atresia (clogged bile causing dystruction of duct), (2) choledocholithiasis (gallstones in the bile), (3) cystic disease
What type of bilirubin is seen in obstruction of the bile duct?
Which 3 lab test are recommended for hyperbilirubinemia in newborns?
(1) serum total and direct bilirubin, (2) blood groups with antibody testing (most common is isoimmunity), (3) hemoglobin and hematocrit determination (to determine the amount of hemolysis)
What are 3 optional lab test are used for hyperbilirubinemia in newborns?
(1) blood smear, (2) reticulocyte count (immature RBC to check for hemolysis ), (3) G6PD screening (seen in middle easterners and causes hemolysis).
What is kernicterus?
it is seen in hyperbilirubinemia in neonates, where changes in neuronal cell populations change when unconjugated exceeds 20mg/dl/day
In kernicterus, what is the clinical feature associated with the neuropathy for bilirubin staining? (1) basal ganglia, (2) brain stem oculuomotor nuclei, (3) brain stem auditory nuclei.
(1) basal ganglia: athetosis (Uncontrolled movements), (2) brain stem oculuomotor nuclei, (3) brain stem auditory nuclei
Other than bilirubin staining, what is the clinical feature associated with the neuropathy of kernicterus (hyperbilirubinemia).
Neuronal necrosis (days later)
What are 8 acute symptoms of hyperbilirubinemia?
Initial: (1) lethargy, (2) hypotonia (decreased muscle tone), (3) weak suck, Progressively, (5) choreo-athetoid cerebral palsy, (6) opisthotonus, (7) sensorineural hearing loss, (8) mental retardation
what is the current treatment in the U.S. for neonatal hyperbilirubinemia?
what is the effect of phototherapy?
structural and configurational isomerization
How do synthetic metalloporphyrins work in controlling hyperbilirubinemia?
They inhibit heme oxygenase, which catalyzes the conversion of heme to biliverdin (this is the rate limiting step). Heme is excreted by an alternate pathway.
How can the amount of bilirubin be measured?
since CO and bilirubin are formed stoichiometrically at a 1:1 molar ratio, you can use CO
Can maturation of glucuonyl transferase activity be used to measure bilibrubin output?
which color light (and wavelength of light) is most effective in phototherapy for hyperbilirubinemia?
Blue, 400-550 nm
What physical property does bilirubin (now sturctual lumirubin) have after phototherapy?
it is more polar and more water soluble.
What are the treatment options for breast fed babies?
(1) increase feeding frequency, (2) phototherapy, (3) temporarily d/c breast feeding while managing phototherapy.
When should newborn first follow up visit take place based upon the following release date after birth? (a) < 24h (b) 24-48h, and (c) 48-72h
(a) < 24h: 3 day, (b) 24-48h: 4 days, and (c) 48-72h: 5 days

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