Hematology and Hyperbilirubinemia Flashcards

Which enzyme is responsible for converting heme to biliverdin in the catabolism of hemoglobin?

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.

A term neonate develops jaundice at 18 hours of age. Which of the following is the MOST likely cause?

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.

At what gestational age does fetal hemoglobin (HbF) begin to be replaced by adult hemoglobin (HbA)?

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.

Which of the following best describes physiologic jaundice in a term neonate?

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.

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?

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.

Which of the following maternal blood types places a neonate at highest risk for significant ABO hemolytic disease?

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.

What is the primary mechanism by which phototherapy reduces serum bilirubin levels?

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.