Hemolytic Disease of the Newborn Flashcards
What is hemolytic disease of the newborn?
Hemolysis in a newborn or fetus caused by blood-group incompatibility between mother and child
What is the mechanism of HDM?
- Baby inherits blood group Ag (from dad) that are foreign to mom
- Baby’s blood gets into mom’s circulation (can happen during delivery or before e.g. tear in placenta)
- Mom makes Ab to baby’s blood group Ag (first pregnancy)
- Mom’s Ab attack baby’s RBCs (second pregnancy)
What blood types must occur for HDN to happen?
- Mom must be Rh -
- Baby must be Rh +
What are 4 big consequences of HDN?
- Extramedullary hematopoiesis
- Heart and liver failure
- Jaundice
- Kernicterus
How does extra medullary hematopoiesis work in HDN?
- It’s the process of trying to make red cells and other hematopoietic cells outside of the hematopoetic space (bone marrow)
- You make the RBCs and other cells in the liver and spleen which can clog up organs and keep them from functioning normally
What does heart and liver failure do in HDN?
- Hydrops (EDEMA - immune edema/hydrops)
- Fluid backs up behind the heart and goes into the tissues
- If liver starts failing because it doesn’t have oxygen things built up, it will die
- Then the body can’t make albumin and fluid will leave vessels and go out into the tissues
What does jaundice do in HDN?
- Yellow color comes from unconjugated bilirubin from the liver
- Many babies are born with a small bit of jaundice & you put them under the lights
- A small degree of bilirubin isn’t damaging
How does phototherapy help babies with jaundice?
- When you put them under the lights, the bilirubin changes conformation in the blood and becomes less toxic
- They don’t get rid of the bilirubin, it’s just changed!
What does Kernicterus do in HDN?
- If you have too much bilirubin it can get into the brain and cause problems
- Insoluble (unconjugated) bilirubin gets into the brain from the liver
- Colors the inner most part of the brain yellow - including the internal capsule
How does Rh incompatibility work?
- Only the D Ag is involved
- Ab response depends on how much Ag mom is exposed to
- Initial exposure evokes IgM (which can’t cross the placenta); first baby usually safe
- Second exposure evokes IgG; second baby may get HDN
How do you diagnose Rh HDN?
DAT (baby) - direct anti-globulin test to see if mom’s antibodies are binding baby’s red blood cells - looking for Abs on RBC surface
IAT (mom) - same as direct anti-globulin test, except you’re looking to see if mom creates anti-Rh antibodies
How do you prevent HDN?
- Rhogam (anti-D Ab - Rhogam can’t cross the placenta)
- –Admin. at 28 weeks
- –Admin within 72 hours after delivery (need to know how much fetomaternal hemorrhage in order to deliver correct dose)
How do you quantify fetomaternal hemorrhage so that you can dose Rhogam?
-Use Kleihauer-Betke test
OR
-Use flow cytometry test
How does the Kleihauer-Betke Test work?
- Make smear of mom’s blood
- Expose smear to acid bath (removes HbA - adult hemoglobin)
- Stain smear
- Baby’s cells appear pink; mom’s appear ghostly
(mom’s cells die but baby cells live and stain bright red)
How does the flow cytometry test for fetal cells work?
- Use mom’s blood
- Apply anti-HbF antibody (if not HgF (baby hemoglobin cells) then there won’t be any result)
- Run flow
- Baby cells, if present, are intensely positive
Fetal cells present: 0.5%
