What occurs in HDFN
When mom is negative and baby is positive, the first pregnancy has mom produce Anti-D from the being exposed to D positive cells
-Maternal anti D are able to cross placenta
-the fetal cells in the next pregnancies are destroyed by AntiD if the baby is Rh pos
-mom is protected with Rh neg against the anti D after delivery
What is the difference between the fisher race theory and Wiener Theory
what is the current theory
Fisher-Race Theory:
A gene complex is inherited that codes for 3 closely linked set of alleles
Wiener Theory:
1 gene is responsible for the expression of all
Rh Blood Group systems
current :Rh Blood Group
System antigens are determined By 2 genes. Allele D or RHCE
What are Rh Genetics
-genes codominant alleles
-RHD= D Ag as heterozygous or homozygous Dd or DD
RHCE genes have 4 alleles at am locus
1) RHCE
2) RHCe
3) RHcE
4) RHce
5 Ag can be found in most ppl
Which AG is most immunogenic
D Ag after A and B antigen
-Anti D is seen only if the pt with D Ag is exposed to D pos cells
-Exposure from pregnancy or transfusions
Rh pos/neg is whether there is D AG on RBC
Rh Antibodies- how are they different from ABO system
1) Red cell immune: DO NOT produce the antibodies unless exposed to red blood cells through transfusion or pregnancy
2) IgG
3) Poor Complement Binding
What is the structure of Rh Ag
- protein structure-amino acids
-Elicits an IgG immunogenic response
-Exposure through transfusion or pregnancy-Red Cell Immune
Not expressed on tissues
Well-developed at birth
Direct gene product (not enzyme)
RHD/RHCE Genes codes directly for antigen
Can easily cause Hemolytic Disease of the Fetus and Newborn (HDFN)
-protein that is made up of over 400 AA and crosses RBC membrane 12 times
-Exposed loops are the AG
-Product of RHD gene and RHCE gene
Rh Phenotype vs. Genotype
D+C+E-c+e+
Antigens Present, Serologically Detectable
DCe/Dce, Dce/dCe, DCe/dce
Genotype- Possible Genes Inherited
most common antibody in RH neg pt vs Rh pos
Anti D in Rh neg
Anti E in Rh pos
Anti e is autoAB hard to find since 98% of pop has e AG
Fisher-Race Nomenclature
- 3 separate genes and their alleles D,C,E, c and e
-linked on the same chromosome and inherited as a gene complex
AG that are possible are D,C,E, c and e
-d is amorphic or deleted gene
-If D antigen is present, the genotype can be either DD or Dd
DCE, DCe, DcE, Dce, dCE, dCe, dcE, dce
Wiener Nomenclature
One gene responsible for the expression of 8 alleles which causes many Rh Ag to be present
-terminology is still used even if the theory was incorrect
Ro, R1, R2, Rz, r, r’, r”, ry
Types of Rh Reagents
Monoclonal Anti-D
Monoclonal Anti-D and Polyclonal Anti-D blend – Must be mixed together for Weak D detection
Monoclonal Anti-D – Low protein diluent (6% bovine albumin) containing IgM
at michener we use Anti-D1 and Anti D2
Polyclonal Anti-D Blend – IgG and IgM
-Low protein diluent doesnt promote false positive agglu that you find with high protein D typing reagents
Types of Rh Reagents
Rh Control
-protein media can cause false pos
-Rh Control – Low protein diluent (6% bovine albumin) but NO anti-D
Purpose – Detects false positive results. To show reaction is due to anti-D NOT diluent
Should be NEGATIVE to report ABO and Rh typing
When would you have a positive Rh control
Positive DAT - AB on the cells (used modified anti D like monoclonal, saline AntiD)
Rouleaux/cold agglutinins - use 3x washed RBCS
Bacterial contamination - repeat
What are three types of weak D
Genetic Weak D
Genetic Weak D
D occurs when there are low AG
Gene codes for less D antigens
Usually needs IAT Weak D testing
Does not usually produce Anti-D
What are three types of weak D
C Trans (positional)
Position effect: C antigen inherited in
trans position to D antigen
Weaker expression of D antigen
Monoclonal Anti-D can detect
Does not usually produce Anti-D
What are three types of weak D
Partial D or Mosaic D
Missing part of the Rh antigen
Mutated gene: change in aa, therefore change in protein
Several variations
Detected by monoclonal Anti-D or may need Weak D testing (IAT)
different results with different antisera (polyclonal vs monoclonal)
Individuals can make Anti-D to the part of the antigen missing
if they are either they need to be treated as Rh neg because you dont want them to produce AB /Anti D
How to detect Weak D?
Antisera
-Immediate spin method may have a Weak Positive results- still call Rh Positive
-Immediate spin method may have a Discrepancy in testing
-If automation is used- discrepancy in D1/D2 testing
Weak D Policies
initial Rh typing on everyone
If the IS Anti-D is negative :
1) Stop if adult patient, result as Rh Negative
2) Perform Weak D testing on ALL Donors (at CBS) if its D1 and D2 neg then you have to know its actually neg
3) Perform Weak D testing on Rh Negative babies of Rh Negative Moms
IF Weak D testing is POSITIVE, then donors and babies are called Rh Positive.
Weak D IAT test
To detect these weaker expressions of
the D antigen, we use the IAT method
- do normal D1,d2 if there is less AG then you can have sensitization without agglutination
-incubate Anti D and wash to remove extra antisera, and add ahg
-the AHG will show agglutination if there is sensitization
NO checking under the Microscope
Add CCC to all negative reactions
minimum reaction should be 1+
Weak D IAT False positive
Weak D testing can be false positive due to in vivo coating of Red cells with IgG antibody
-Rh control is positive
-AHG reacts with the IgG on the RBC membrane even if there is not Anti D attached
-invalid weak D testing
Auto Antibody, Mom’s Antibody on Fetal
cells, and Patient Antibody on donor cells.
Molecular Testing for Weak D
policy for testing
- prenatal pts with weak serological RHD results were RHD genotyping can modify their blood product or RhIG needs
-pt that need chronic transfusions or have complex needs where genotyping can change blood requirements
-pt who appear serologically D positive but need to be transfused with AntD
-mosiac D is most important because the pt can produce Anti D
how to select Rh for transfusion
- Rh AB are red cell immune
-Rh neg ppl dont automatically make Anti D
-Rh neg pts can be given Rh pos RBC once safely the AB is produced quickly - antigenic
-Anti D is an IgG and doesnt bind complement so hemolysis is extravascular (5-10 days)
-C, E, c, or e antigens not considered unless the pt has corresponding AB
What are ABO ABs
non red blood cell stimulated
-most clinially significant
-ppl have ABO AB for the AG they lack
-IgM
-activate complement, only one IgM is needed to initiate complement pathway
* Immediate Cell Lysis
* Intravascular Hemolysis
-can cause severe transfusion reactions
Landsteiner’s Rules
1) A person does not have the antibody to their own antigen.
2) Each person has antibodies to the antigen, they lack (only in the ABO system)
