NNP Hematology and Hyperbilirubinemia 1 — Questions and Answers
Question 1: Which enzyme is responsible for converting heme to biliverdin in the catabolism of hemoglobin?
- Biliverdin reductase
- Heme oxygenase (Correct answer)
- UDP-glucuronosyltransferase
- Glutathione peroxidase
Correct answer: Heme oxygenase
Heme oxygenase cleaves the heme ring to produce biliverdin, carbon monoxide, and free iron, which is the first step in bilirubin production.
Question 2: A term neonate develops jaundice at 18 hours of age. Which of the following is the MOST likely cause?
- Breast milk jaundice
- Physiologic jaundice
- ABO incompatibility hemolytic disease (Correct answer)
- Crigler-Najjar syndrome type II
Correct answer: ABO incompatibility hemolytic disease
Jaundice appearing within the first 24 hours of life is pathologic and most commonly caused by hemolytic disease such as ABO incompatibility.
Question 3: At what gestational age does fetal hemoglobin (HbF) begin to be replaced by adult hemoglobin (HbA)?
- 20–24 weeks gestation
- 28–32 weeks gestation
- 32–34 weeks gestation
- After 34–36 weeks gestation (Correct answer)
Correct answer: After 34–36 weeks gestation
The switch from HbF to HbA production begins at approximately 34–36 weeks gestation and continues postnatally over the first 6 months of life.
Question 4: Which of the following best describes physiologic jaundice in a term neonate?
- Onset within 24 hours, peak by day 2
- Onset after 24 hours, peak by day 3–4, resolves by day 14 (Correct answer)
- Onset after 24 hours, persistent beyond 3 weeks
- Onset at day 5–7, associated with breastfeeding difficulty
Correct answer: Onset after 24 hours, peak by day 3–4, resolves by day 14
Physiologic jaundice in term neonates typically appears after 24 hours, peaks on days 3–4, and resolves by day 14, driven by increased bilirubin production and immature conjugation.
Question 5: A 3-day-old breastfed neonate has a total serum bilirubin (TSB) of 18 mg/dL. The mother reports the infant is nursing 8–10 times per day with adequate wet diapers. What is the MOST appropriate next step?
- Discontinue breastfeeding and start formula
- Begin phototherapy based on hour-specific nomogram (Correct answer)
- Perform exchange transfusion immediately
- Obtain a direct Coombs test only and observe
Correct answer: Begin phototherapy based on hour-specific nomogram
Management of neonatal hyperbilirubinemia should be guided by the AAP hour-specific nomogram, which determines phototherapy thresholds based on age in hours and risk factors.
Question 6: Which of the following maternal blood types places a neonate at highest risk for significant ABO hemolytic disease?
- Type A mother with type B infant
- Type O mother with type A or B infant (Correct answer)
- Type B mother with type O infant
- Type AB mother with type A infant
Correct answer: Type O mother with type A or B infant
Type O mothers have naturally occurring anti-A and anti-B IgG antibodies that can cross the placenta and cause hemolysis in type A or B infants.
Question 7: What is the primary mechanism by which phototherapy reduces serum bilirubin levels?
- Enhances hepatic UDP-glucuronosyltransferase activity
- Converts unconjugated bilirubin to water-soluble photoisomers excreted without conjugation (Correct answer)
- Increases intestinal motility to reduce enterohepatic circulation
- Promotes renal excretion of unconjugated bilirubin
Correct answer: Converts unconjugated bilirubin to water-soluble photoisomers excreted without conjugation
Phototherapy converts unconjugated bilirubin in the skin to structural and configurational isomers (lumirubin and photobilirubin) that are water-soluble and can be excreted in bile and urine without hepatic conjugation.
NNP Hematology and Hyperbilirubinemia 1
Which enzyme is responsible for converting heme to biliverdin in the catabolism of hemoglobin?