Lecture 6: Haemolytic Disease of the Newborn (HDN) Flashcards
Define HDN and its primary cause.
Destruction of fetal/neonatal RBCs by maternal IgG antibodies crossing the placenta. Most severe cases involve anti-D (Rh) or anti-A/B (ABO).
Why is ABO HDN generally milder than Rh HDN?
Fetal RBCs express fewer A/B antigens, and maternal anti-A/B are partially neutralized by soluble A/B substances in fetal plasma.
Explain the two mechanisms of maternal sensitization to Rh(D).
Antibody adsorption: Maternal anti-D IgG crosses placenta in subsequent pregnancies.
Fetomaternal hemorrhage (FMH): Fetal RBCs enter maternal circulation during delivery/trauma, triggering anti-D production.
What is the role of anti-D prophylaxis?
Given to Rh(D)− mothers post-delivery/miscarriage to clear fetal Rh(D)+ RBCs before maternal immune response occurs (prevents sensitization).
What does a positive DAT (Direct Coombs test) indicate in HDN?
Maternal antibodies (e.g., anti-D) are bound to fetal RBCs → confirms immune-mediated haemolysis.
How does the Kleihauer-Betke test work?
Acid elution stains HbF (fetal cells = pink) vs. maternal HbA (ghost cells). Quantifies FMH volume.
What FBC findings suggest HDN?
↓Hb, ↑reticulocytes, ↑unconjugated bilirubin, nucleated RBCs on film.
What is kernicterus?
Severe unconjugated bilirubin (>20 mg/dL) crosses blood-brain barrier → neuronal damage (lethargy, seizures, death).
Name three treatments for HDN.
Phototherapy: Converts bilirubin to water-soluble form.
Exchange transfusion: Removes antibody-coated RBCs/bilirubin.
IVIG: Blocks antibody-mediated destruction.
Which non-Rh antibodies can cause HDN? Rank by severity.
Anti-Kell (severe; suppresses erythropoiesis).
Anti-c (mild-severe).
Anti-E (usually mild).
Why do Lewis system antibodies not cause HDN?
They are IgM (cannot cross placenta) and antigens are poorly expressed on fetal RBCs.
