HDFN Flashcards
Destruction of RBCs of the fetus by antibodies produced by the mother
Hemolytic Disease of the Fetus and Newborn (HDFN)
What class of Ig is actively transported across the placenta?
IgG
How much blood is needed to immunize the mom?
1 ml (20 drops)
What is the factor that affects immunization and severity?
Fetomaternal hemorrhage during pregnancy
What occurs during fetomaternal hemorrhage during pregnancy?
Significant increases in maternal antibody titers leading to increased severity of HDFN
What method is used to determine fetal hemoglobin?
Acid-elution
What increases the risk of fetomaternal hemorrhage?
Amniocentesis, chorionic villus sampling, and trauma to the abdomen
When does active transport of IgG begin?
Second trimester and continues until birth
Which immunogen is the most antigenic?
D
What are other potent Rh immunogens of HDFN?
C, c, E
What is the most clinically significant non-Rh antibody able to cause HDFN?
Anti-K
Do you still work up Anti-Lewis for HDFN?
Yes
What are the common antibodies identified in prenatal specimens that cause HDFN?
Rh series and Kell
What the rare antibodies identified in prenatal specimens that cause HDFN?
Anti-Fya, Anti-Jka, Anti-MNSs
What antibodies never cause HDFN?
Anti-Lewis, I, IH, P1
What happens during hemolysis in HDFN?
Maternal IgG attaches to specific antigens of fetal RBCs –> the antibody coated cells are removed by macrophages of the spleen
What is the rate of destruction of fetal RBCs when the maternal IgG attaches?
Depends on antibody titer and specificity
What happens during RBC destruction?
Release of hemoglobin, which metabolizes bilirubin
What is done during the first prenatal visit (1st trimester)?
Type and screen (including weak D)
What must be able to be detected during type and screen?
Clinically significant IgG alloantibodies reactive at 37C and in antiglobulin phase
What happens if the screen is negative during the 1st prenatal type and screen?
Repeat testing prior to RhIg therapy (28 weeks/3rd trimester)
What happens if the screen is positive during the 1st prenatal type and screen?
Antibody must be identified
- can ignore IgM antibodies
What happens when the screen was initially negative but now positive during the/after the 28-week mark?
Reactive anti-D due to RhIg immunization
What should the father be tested for?
Presence of D antigen
What test should be done if the mother has anti-D and the father is heterozygous for D antigen?
Amniocentesis to check if baby is carrying D antigen, which can be performed as early as 10-12 weeks
What does the antibody titration tell you?
Antibody titration tells you the concentration of alloantibody
What is done during an antibody titration?
Patient serum containing antibodies is serially diluted and tested against RBCs to determine the highest dilution at which a reaction occurs (MUST USE MONOCLONAL ANTI-IgG AHG FOR IAT)
What is the result of the titration reported as?
A reciprocal of the titration endpoint
What titration is considered significant?
Titer of 16-32
What is it called when a fetus receives a blood transfusion through the umbilical vein in the placenta?
Intrauterine Transfusion
What is the goal of a intrauterine transfusion?
To maintain fetal hemoglobin above 10 g/dL
How often do you need to repeat intrauterine transfusion once initiated?
Every 2-4 weeks until 34-36 weeks gestation (or until fetal lungs are mature)
What can intrauterine transfusion suppress?
Fetal bone marrow production of RBCs, so infant may need a transfusion after birth
What serological tests are performed on a newborn?
ABORh (without reverse) & DAT with IgG reagent
What type of AHG reagent is used in a DAT for a newborn?
Monoclonal IgG AHG
Why is reverse typing not performed on a newborn?
Newborn’s isoagglutinins are the mother’s so there’s no point
What happens when there’s a false negative RhD for the baby?
Since baby’s RBCs are heavily bound with maternal anti-D, an ELUATE is needed to type the baby’s RBCs for anti-D
What happens when baby has a positive DAT?
There’s maternal IgG antibody coating infant’s RBCs, which causes false negative RhD
What causes the false negative RhD for the baby?
If the baby’s D antigens are already bound to mom’s anti-D, it seems like there’s no D antigen for the D antisera to bind to.
Why does a positive DAT invalidate Rh typing of baby?
Because it creates a false negative. There are anti-D antibodies attached to the D antigen, but it’s just not showing up.
What is used to correct anemia when bilirubin level is not high enough to warrant an exchange transfusion?
Small aliquot transfusions
What is used to remove high levels of unconjugated bilirubin?
Exchange transfusions
What is done to prevent kernicterus (brain damage caused by bilirubin buildup) in newborns?
Exchange transfusions
What else does exchange transfusions do besides remove bilirubin?
- Remove antibody-coated RBCs of the baby, thereby preventing their destruction in vivo and an increase in bilirubin
- Remove maternal antibody in circulation, preventing it from destroying newly produced RBCs
- Correct anemia without causing volume overload
Who is more affected at lower concentrations of bilirubin?
Premature infants rather than full-term infants
What type of blood is often used for intrauterine and neonatal transfusions?
Type O
What are the requirements for the blood used for intrauterine transfusions?
Type O NEG RBCs must be antigen-negative, CMV negative, less than 7 days old, irradiated to prevent GvHD, negative for HGB S, and compatible with mother’s plasma
What units are given for fetuses and neonates whose blood types are unknown or Rh-negative?
Rh-negative units
What should the hematocrit level of RBCs be for intrauterine transfusions?
more than 70%
What type of blood preferred for exchange transfusions?
RBCs from WB units, IRRADIATED to prevent graft vs host disease, NEGATIVE for Hgb S, and LESS than 7 days old
What type of plasma is used during exchange transfusions?
Plasma from group AB (no antibodies)
What does RhoGam do?
Attaches to fetal Rh-positive RBCs in maternal circulation to prevent her from reading them and creating anti-D; so it only prevents cases due to anti-RhD
When is RhoGam given?
28 weeks
When is the dose present in screen?
10% of the antenatal dose will be present at 40 weeks gestation
What calls for administration of RhoGam postpartum?
If the mom is non-immunized, Rh-negative & the baby is Rh positive (or weak D positive)
Should you still give a non-immunized, Rh-negative mom RhoGam if she has a stillborn/miscarriage/abortion?
Yes, since baby’s blood type is unknown, just in case
What happens if you don’t give Rh-negative mom RhoGam after delivery?
It’ll result in active immunization, so give within 72 hours of delivery
Does administration of RhoGam count as active immunization?
No, it’s PASSIVE IMMUNIZATION and should NOT be mistakenly interpreted as active immunization; so while anti-RhD might be detected during delivery, an additional dose of RhoGam should still be given (if it’s really passive and no active)
How must of a dose of RhoGam must be administered to all non-immunized, Rh-negative moms that give birth of Rh-positive babies?
300 ug (30cc) to protect against 1.5mL of pRBCs or 30mL of WB
What is the total fetal blood volume at 12 weeks?
less than 5mL
What is the dosage given for abortions or ectopic pregnancies?
Mini dose of 50 ug (less than 5cc)
What is the Kleihauer-Betke Test for?
A quantitative test that estimates the amount of fetal-maternal hemorrhage (bleeding)
When should more than one dose of RhoGam be administered?
When the degree of FMH (fetal maternal hemorrhage) is greater than 30mL of WB
What is a screen test used to determine presence of a FMH?
Rosette Test
What happens when the Rosette Test is positive?
Kleihauer-Betke test is needed to calculate the amount of fetal-maternal hemorrhage (bleeding)
What is the limitation of Rosette Screening test?
The FMH must be 10cc or more and the mom has to be RhD-negative and the baby has to be RhD-positive
What is the formula of Kleihauer-Betke?
[(fetal cells/total cells) x 5000mL] / 30mL = # of Rh doses/vials needed
**Rounded up or down then ADD 1 VIAL EXTRA*
When is ABO HDFN often seen?
First pregnancy
When is Rh HDFN often seen?
Second pregnancy
What is the IgG seen in ABO HDFN?
Anti-A,B
What are the IgG often seen in Rh HDFN?
Anti-D, Rh series, Kell
During ABO HDFN, what is the range of bilirubin seen at birth?
Normal
During Rh HDFN, what is the range of bilirubin seen at birth?
Elevated
Is there anemia at birth for ABO HDFN?
No
Is there anemia at birth for Rh HDFN?
Yes
What is phototherapy used for?
For slowly rising bilirubin levels; to convert unconjugated bilirubin in both ABO and Rh HDFN and have it excreted in the urine
Is exchange transfusion common in ABO HDFN?
Rare
Is exchange transfusion common in Rh HDFN?
Sometimes
Is intrauterine transfusion common in ABO HDFN?
No
Is intrauterine transfusion common in Rh HDFN?
Sometimes
Who is most at risk for ABO HDFN?
A (white) or B (black) infants with O mothers with potent anti-A,B
Does mother’s history of prior transfusions or pregnancies relate to the occurrence and severity of ABO HDFN?
No
What is exchange transfusion with O RBCs used for?
Rapidly increasing bilirubin levels
When does bilirubin peak?
1 to 3 days
What happens if you keep giving the baby blood during intrauterine transfusion?
You can suppress fetal bone marrow production of RBCs, so the baby may need a transfusion after birth
Are high-titered IgG antibodies capable of causing significant RBC destruction in an ABO-incompatible fetus?
No, results in mild anemia or normal hgb levels
When will ABO antigens be fully developed?
1 year after birth
What is the number one cause of HDFN now?
ABO incompatibility in A or B babies with O mothers
Does the severity of HDFN depend on positive DAT; or anti-A, anti-B, or anti-A,b in eluate of infant RBCs?
No
