Hemolytic Disease of the Newborn - Krafts

Question 1

What causes a hemolytic disease of the newborn?

Answer 1

• Blood-group incompatability between mother and child
  
  • baby inherits a blood antigen that mom doesn’t have → so mom creates antibodies in response to attack the antigen

Question 2

What is the four step mechanism of Hemolytic Disease of the Newborn?

Answer 2

1. Baby inherits blood group antigen (from dad) that is foreign to mom
2. Baby’s blood gets into mom’s circulation
3. Mom makes antibodies to baby’s blood group antigen
4. Mom’s antibodies attack baby’s RBCs

Question 3

What antibody is too big to cross the placenta? It switches to what?

Answer 3

• Mom initially will make IgM = too big to cross the placenta
• IgM class switches to IgG later to cross the placenta and attack baby’s cells

Question 4

What are the consequences of Hemolytic Disease of the Newborn?

Answer 4

• Extramedullary hematopoesis
  
  • cells mature in other places than the bone marrow
  • can clog up vessels and block stuff
• Heart and liver failure
  
  • blood backs up behind heart
  • goes into tissues due to low hydrostatic pressure
  • liver does not get enough O₂, stops making albumin, pressure in vessels unbalanced, fluid moves into tissues
• Jaundice
• Kernicterus
  
  • unconjugated bilirubin enters the brain
  • neonates do not have well developed BBB

Question 5

What is the only antigen involved in Rh Incompatibility?

Answer 5

D Antigen

• Rh factor = D antigen
• Can get 1 of 2 alleles:
  
  • D → Do make the D antigen (so Rh+)
  • d → Do NOT make the D antigen (so Rh-)

Question 6

What does the antibody response from mom depend on in Rh Incompatibility?

Answer 6

Antibody response depends on how much antigen mom is exposed to.

Question 7

What does the initial exposure evoke with Rh Incompatibility?

Answer 7

• Intial exposure → evokes IgM
  
  • can’t cross placenta
  • first baby usually safe

Question 8

What does the second exposure evoke in Rh Incompatability?

Answer 8

• Second exposure evokes IgG
  
  • second baby may get HDN

Question 9

How do you diagnose Rh Hemolytic Disease of the Newborn?

Answer 9

• DAT on baby
  
  • look for antigens
• IAT on mom
  
  • look for anti-Rh antibodies

Question 10

How can you Prevent Rh HDN?

Answer 10

• Rhogam
  
  • anti-D antibody (anti-Rh antibody that binds to surface of baby’s Rh⁺ RBCs to make invisible to mom)
  • administered at 28 weeks & within 72 hrs of delivery
  • must quantify amount of fetomaternal hemorrhage to dose Rhogam

Question 11

How do you quantify the amount of fetomaternal hemorrhage in order to dose Rhogam?

Answer 11

• Kleihauer-Betke test
  
  • expose acid to mom’s blood smear and count pink baby’s RBCs (mom’s become ghostly)
• Flow cytometry
  
  • detects anti-HbF antibody

Question 12

How common is ABO Incompatibility?

Answer 12

• 25% of pregnancies
  
  • only severe in 1 in 200 cases

Question 13

Why isn’t ABO Incompatibility more of a problem in pregnancy?

Answer 13

• Most anti-A and anti-B antibodies = IgM
• Neonatal RBCs express A and B poorly
• Many cells besides RBCs express A and B antigens
  
  • ​thus sopping up some of mom’s antibodies
• There is no effective protection against ABO-mediated HDN.

Question 14

What is the treatment for Hemolytic Disease of the Newborn?

Answer 14

• Mild cases: Phototherapy
  
  • light changes confirmation of unconjugated bilirubin so that it is not toxic
• Severe cases: total exchange transfusion
• Mom can undergo plasmapheresis
• High-dose intravenous immunoglobulin