BB - HDFN, RhoGAM Flashcards
HDFN is caused by maternal antibodies crossing the ___ to attack fetal RBCs. The maternal antibodies are in the class…
Placenta
IgG
Maternal antibodies target fetal antigens inherited from…
The father
-mother does not make antibodies against her “own” antigens
Causes of HDFN is classified into 3 different categories
Caused by anti-D hemolytic disease
Caused by antibodies against other antigens (ie anti-c, anti-K)
Caused by ABO hemolytic disease
ABO hemolytic disease is caused by these antibodies… made by a mother of this ABO type… What immunoglobulin class are they?
anti-A, anti-B or anti-A,B
-commonly anti-A,B since majority are IgG
Group O mothers
IgG
-usually, they are IgM, but in this case, they’re IgG, so they can cross the placenta
3 stages of HDFN testing
Prenatal screening
Cord blood work-up
Post partum work-up
Prenatal screening - what tests are involved for the mother?
ABORh (D)
Antibody screen
Antibody ID panel if screen is positive
Why would we want to do multiple antibody titers during pregnancy?
To determine if the titer is rising
- amniocentesis if significant titer rise
- antibody titrations on mother’s plasma
Cord blood work-up involves these tests. Should we do reverse typing?
Cord cells typed AFTER BIRTH:
ABORh (D)
DAT
No reverse typing
- baby has maternal antibodies
- baby does not produce own antibodies yet
What should we do next if the cord cells are DAT positive?
Perform an eluate from cord cells
Do an antibody ID from eluate (screens rarely done)
Post partum work-up involves these tests for the mother
ABORh (D)
Antibody screen
Antibody ID panel
Additional post partum work-up for an Rh negative mother and an Rh positive baby is this screening test… What does the test look for in maternal circulation?
Rosette Screen
Presence and amount of fetal cells
A positive Rosette screen is followed up by the ___ test. The test is useful for calculating…
Kleihauer-Betke test
The dose of Rh immune globulin to give
Why must cord blood cells be washed so much?
To remove Wharton’s Jelly
If the mother had no unexpected antibodies, what other reason could explain HDFN?
ABO hemolytic disease
When doing an antibody ID panel for both mother and baby to identify an unexpected antibody, should we use different cell numbers/lots or the same cells?
Same
What can we conclude if the same panel cells react to both mother’s serum and baby eluate?
Maternal alloantibodies attached to baby’s RBCs
The Kleihauer-Betke test utilizes this concept as a way to enable fetal RBCs to be recognized
Fetal hemoglobin (hemoglobin F) is resistant to acid elution -resistant to staining
What is the ultimate purpose of the Rosette test? A positive Rosette screening test should be followed up with…
Provide indication if bleeding was larger than normal
-test does NOT provide evidence that increased dose of RhoGAM is required to protect mother from producing anti-D; do KB test
More cumbersome Kleihauer-Betke quantitative test
-determines dose of RhoGAM to give
The Rosette test requires these components
Maternal blood -D negative mother -contains D positive fetal cells Anti-D Ficin-treated D positive RBCs
Fetal D+ RBCs will be surrounded by indicator D+ cells, making them easier to see
Rosette test - what do the positive and negative results look like?
Positive = 3 or more clumps
Negative = 2 or fewer clumps
The most clinically significant non-Rh system antibodies that cause HDFN are…
Anti-Kell
HDFN is this type of hemolysis
Extravascular
- maternal IgGs attach to antigens on fetal RBCs
- removed by macrophages in spleen
RBC hemolysis releases hemoglobin, which metabolizes to ___. Buildup causes damage to this organ…
Bilirubin
Brain
-sunbathe or put under UV light to clear bilirubin from baby
Clinically significant alloantibodies are reactive at these 2 stages of the screening test
37C
AHG
- clinically significant alloantibodies = IgG
- Rh typing/weak D
At what stage of pregnancy is RhoGAM given prophylactically? Postpartum?
28 weeks
Within 72 hours
If mother is already making anti-D, what test can we perform to determine if it’s from an active or passive immunization?
Titration
- titer >= 4 is active
- titer < 4 is passive
Clinically significant titer levels
16-32
When a baby has a positive DAT, can we determine the Rh typing? Why or why not? What other testing can we do?
No
Baby’s RBCs are covered with mother’s antibodies. Might give false negative
Eluate
What is the KB test calculation to determine the total volume of fetomaternal hemorrhage?
(# fetal cells * maternal blood volume) / # maternal cells = volume of fetal whole blood (in ml)
The standard 300 ug dose of RhoGAM is sufficient to suppress Rh immunization of how much fetal blood?
15 ml fetal RBCs (30 ml whole blood)
If 15 ml of fetal whole blood was calculated in the KB test, how many vials of RhoGAM should be given?
15 ml / 30 ml = 0.5
Round up to 1
Give an additional vial
Total vials = 2
1 vial of RhoGAM covers 30 ml of fetal whole blood
ABO HDFN - O mothers almost always target fetus with type…
A or B
- A in white population
- B in black population
Assuming an elution has been performed correctly and antibodies have been removed from cells, the antibody screen using the last wash should be ___, while the antibody screen using the eluate should be ___. Which one serves as the control?
Negative
Positive
Last wash serves as the control
To do an ABO HDN test, we must use these 3 test cells… The antibodies are from this source…
A1, B and O cells
Eluate
-include a set of last wash control tubes as well
Antibodies can be eluted from RBCs using these methods (3)…
Heat
Organic solvents
High/low pH
Should potentiators like LISS or bovine albumin be added to the eluate?
No, eluate already a low ionic substrate
What does a positive final wash screen indicate?
Insufficient washing when preparing the eluate
- antibodies present in eluate may be from free antibodies in serum
- redo eluate procedure
The goal of an intrauterine transfusion is to maintain a hemoglobin level above… Why would we want to avoid continuous intrauterine transfusions?
10 g/dL
Suppresses fetus’s bone marrow production of RBCs
-stop at 34 weeks
High levels of bilirubin in newborns can be removed through this transfusion…
Exchange transfusion
-removes some maternal antibodies, sensitized RBCs
