Alloimmunization Flashcards
Rh and non Rh alloimmunization
How do you define alloimmunization?
Alloimmunization are antibodies created against antigens found in other humans. For example red cell alloimmunization is an antibody against red cell antigens found in other humans.
What is indirect Coomb’s tests?
It is the same as type and screen. An antibody is used to assess if there are other antibodies present.
What are possible sources of alloimmunization to the D antigen group?
blood transfusion
Pregnancy
IV drug use
Tattoos
What red cell antigen comprise the D antigen in group?
D E c C e
What are the fetal risks in an alloimmunized pregnancy?
Red cell hemolysis or erythroblastocysis leading to significant anemia
Preterm delivery
Intrauterine percutaneous blood sampling
What is the cause of fetal anemia in an alloimmunized pregnancy?
Hemolysis from antibody mediated reaction
What is hemolytic disease of a newborn?
Hemolysis mediated by antibodies due to incompatibility.
A, B, AB, O incompatibility.
Rh negative mother with a Rh positive child
When a positive antibody screen is identified, what are the next steps in your evaluation of the patient?
Obtain an antibody titer
What is the mode of inheritance for red cell antigens?
Autosomal co-dominant
If the father of the baby is homozygous for red cell antigen of interest, what is the likelihood of the fetus being at risk for hemolytic disease of the newborn?
100% - it is high if mother is alloimmunized
If the father of the baby is heterozygous for red cell antigen of interest, what is likelihood of the fetus being at risk for hemolytic disease?
50% chance that the fetus is at risk for the hemolytic disease
How can you determine fetal red cell antigen status?
Amniocentesis -> use PCR typing (100% specificity, false negative rate is low 1-3%), NIPT -> 99% accuracy
If the fetal red cell antigen status is unknown, how will you follow the patient if this is her first alloimmunized pregnancy?
titer every month
MCA with titer 1:8 - 1:32
PUBS with MCA >1.5 MoM
If the fetal red cell antigen status is unknown, how will you follow the patient if this is a subsequent alloimmunized pregnancy?
If it is the same father, there is a 50-100% chance of fetal antigen expression depending on if the father is homozygous or heterozygous.
-MCA dopplers if: previous prenatal loss, previous neonatal exchange transfusion, previous IUT and same father in subsequent pregnancy
What is the role of antibody titers in a first alloimmunized pregnancy?
To determine need for fetal anemia assessment
What is the role of antibody titers in a subsequent alloimmunized pregnancy?
If there was previous prenatal loss, previous neonatal exchange transfusion, previous IUT and same father in subsequent pregnancy then there is NO role
What do you consider to be a critical titer?
1:8 - 1:32
Once a critical titer is identified, how does your management change?
Weekly MCA PSV Dopplers starting at 16 weeks
How do MCA identify anemia?
The concept is related to brain sparing in the setting of fetal anemia.
Describe how you perform a MCA Doppler PSV assessment:
1) Use color doppler at the level of the BPD near the sphenoid bone to locate the MCA vessel closet to the transducer
2) Use pulse wave doppler where the vessel arises from the carotid siphon
3) the angle of the pulse wave should not be more than 30 degrees
What does an MCA PSV >1.5MoM indicate?
Moderate to severe anemia. Fetal Hbg of 6 or less
How do you manage the patient if an MCA PSV is > 1.5MoM at 20 weeks?
PUBS if anemic, then transfuse. Less likely to be successful at this gestational age
How do you manage the patient if an MCA PSV is > 1.5MoM at 30 weeks?
PUBS, if anemic, then transfuse.
How do you manage the patient if an MCA PSV is > 1.5MoM at 36 weeks?
Discuss with neonatology re transfusion prior to delivery
What are the risks of fetal blood sampling?
Bradycardia Rupture of membrane Infection Bleeding Pregnancy loss
Describe how a fetal blood sampling is performed
Placental umbilical cord insertion preferred. Use umbilical vein to decrease the risk of fetal bradycardia. Don’t transfuse if hematocrit is greater than 30%.
Goal HCT is between 35-40%
When do you recommend delivery in an alloimmunized patient in her first alloimmunized pregnancy who has not reached critical titers?
39 weeks
When do you recommend delivery in an alloimmunized patient in her first alloimmunized pregnancy who has reached critical titers but MCV <1.5 MoM?
37- 38 weeks
When do you recommend delivery in an alloimmunized patient in her first alloimmunized pregnancy who has had fetal transfusion?
transfuse up to 35 weeks and deliver between 37-38 weeks
What red cell antigens comprise the non D antigen group?
Duffy Kid Kell MNSs P ----------- Lewis Lutheran
Which non D antigens are not associated with hemolytic disease of newborn?
Lewis and Lutheran
What are possible sources of alloimmunization to the Kell antigen?
Blood transfusion
Why does Kell antigen cause greater risks for fetal anemia?
Kell inhibits erythroid progenitor cell production in the bone marrow
When a positive antibody screen is identified, what are the next steps in your evaluation of the patient?
Obtain maternal titer which assesses the amount of antibody present
If the fetal red cell antigen status is unknown, how will you follow the patient if this is her first alloimmunized pregnancy?
Maternal titer
If the fetal red cell antigen status is unknown, how will you follow the patient if this is a subsequent alloimmunized pregnancy?
If no previous IUT, neonatal transfusion or fetal demise with same father then maternal titer; however if the above is present then MCA PSV
What titer do you consider to be critical for Kell antibody?
1:8
How does management of a Kell alloimmunized pregnancy differ from management of other non-D red cell antibodies associated with hemolytic disease of the newborn?
Follow titers and start MCV PSV if titer is greater than 1:8
