Transcript ABO Blood Group System

ABO Blood Group System
Importance of
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ABO system
ABO compatibility between donor cell and patient
serum is the essential foundation of pre-transfusion
testing
It is the only system with expected antibodies
Whether they are IgG or IgM, ABO antibodies can
activate complement readily
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This means that incompatibilities can cause life threatening
situations (transfusion reactions)
ABO antigens
Biochemical & Genetic Considerations
ABO and H Antigen Genetics
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Genes at three separate loci control the occurrence and location of
ABO antigens.
The presence or absence of the A, B, and H antigens is controlled
by the H and ABO genes.
The presence or absence of the ABH antigens on the red blood
cell membrane is controlled by the H gene.
The presence or absence of the ABH antigens in secretions is
indirectly controlled by the Se gene.
H Antigen
The H gene codes for an enzyme that adds the sugar fucose to the
terminal sugar of a precursor substance (PS)
The precursor substance (proteins and lipids) is formed on an
oligosaccharide chain (the basic structure)
Type I and Type II Precursors
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There are two potential precursors substances for ABH antigens
Type I and Type II
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Both are comprised of identical sugars but the linkage of the
terminal sugars differs in the two types
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Type I precursor has a terminal galactose linked to a
subterminal N-acetylgluosamine in a 1-3 linkage. These same
sugars combine in a 1-4 linkage in type II precursor.
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ABH Ags on red cells are derived from Type II chains whereas
the ABH Ags in plasma are made from both types I & II
precursors
RBC Precursor Structure
RBC
Glucose
Precursor
Substance
(stays the
same)
Galactose
N acetylglucosamine
Galactose
Formation of the H antigen
RBC
Glucose
Galactose
H antigen
N-acetylglucosamine
Galactose
Fucose
H antigen
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The H antigen is the foundation upon which A and B
antigens are built.
A and B genes code for enzymes that add a sugar to the
H antigen
A and B Antigen
The “A” gene codes for an enzyme (transferase) that
adds N-acetylgalactosamine to the terminal sugar of the
H antigen “1-3 N-acetylgalactosaminyltransferase”
The “B” gene codes for an enzyme that adds Dgalactose to the terminal sugar of the H antigen “ 1-3 Dgalactosyltransferase”.
Formation of the A antigen
RBC
Glucose
Galactose
N-acetylglucosamine
Galactose
Fucose
N-acetylgalactosamine
Formation of the B antigen
RBC
Glucose
Galactose
N-acetylglucosamine
Galactose
Fucose
Galactose
Genetics
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The H antigen is found on the RBC when you have the Hh or
HH genotype, but NOT from the hh genotype
The A antigen is found on the RBC when you have the Hh,
HH, and A/A, A/O, or A/B genotypes
The B antigen is found on the RBC when you have the Hh,
HH, and B/B, B/O, or A/B genotypes.
The O allele
– Why do Group O individuals have more H antigen than
the other groups?
– The O gene is a silent allele. It does not alter the structure of
the H substance….that means more H antigen sites.
A
A
Group O
Group A
A
Group O
Many H
antigen sites
A
Group A
Fewer
H antigen
sites
A
Most of the H antigen sites in a
Group A individual have been
converted to the A antigen
Other ABO conditions
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Bombay Phenotype (Oh)
Inheritance of hh
The h gene is an amorph and results in little or no
production of L-fucosyltransferase
Very rare
Bombay
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The hh causes NO H antigen to be produced
Results in RBCs with no H, A, or B antigen (patient types as O)
Bombay RBCs are NOT agglutinated with anti-A, anti-B, or
anti-H (no antigens present)
Bombay serum has strong anti-A, anti-B and anti-H,
agglutinating ALL ABO blood groups
What blood ABO blood group would you use to transfuse this
patient??
Another Bombay
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Group O RBCs cannot be given because they still have the H
antigen
You have to transfuse the patient with blood that contains NO
H antigen
ABO Antibodies
ABO antibodies
RBC Phenotype Frequency (%)
Serum Ab
A
43
Anti-B
B
9
Anti-A
AB
4
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O
44
Anti-A,B
ABO antibody facts
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Complement can be activated with ABO antibodies (mostly IgM,
some IgG)
High titer: react strongly (4+)
Anti-A, Anti-B, Anti-A,B
Clinically Significant
Yes
Abs class
IgM, less IgG
Thermal range
4 - 37
HDNB
Yes
Transfusion Reactions
Extravascular
Intravascular
Yes
Yes
The Rhesus (Rh) Blood Group system
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Rh Genetics: The genes that control the system
are autosomal codominant located on the short
arm of chromosome 1.
D antigen – 85%
d antigen – 15%
C antigen – 70%
c antigen – 80%
E antigen – 30%
e antigen – 98%
Rh Positive
Rh Negative
The presence or absence of D Ag determines if the person is
Rh+ or Rh-
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Rh Deleted : Red cells that express no Ags at the C &
E loci (D)
Number of D Ags greatly increase
Anti-D IgG Abs can agglutinate these cells
RH null: individual that appears to have no Rh
antigens ( -, -, -)
Must use autologous blood products
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No D, C, c, E, e antigens present on the RBC membrane
Rh antibodies
Rh Abs
Clinically Significant
Yes
Abs class
IgG
Thermal range
4 - 37
HDNB
Yes
Transfusion Reactions
Extravascular
Intravascular
Yes
No
Hemolytic disease of the Newborn (HDN)
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Usually related to D antigen exposure and the
formation of anti-D
Usually results from D negative female and D
positive male producing and offspring.
– The baby will probably be D positive.
1st pregnancy not effected, the 2nd pregnancy and
on will be effected-results in still birth, severe
jaundice, anemia related to HDN.
To prevent this occurrence the female is
administered RH-IG.
Rh factor
First pregnancy
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Rh factor can cause
complications in some
pregnancies.
Mother is exposed to Rh
antigens at the birth of
her Rh+ baby.
Placenta
Rh+ antigens
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Mother makes anti-Rh+
antibodies.
Anti-Rh+
antibodies
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During the mother’s next
pregnancy, Rh
antibodies can cross the
placenta and endanger
the fetus.
Possible
subsequent
pregnancies
Weak D Phenotype
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Most D positive RbC’s react macroscopically with Reagent antiD at immediate spin
– These patients are referred to as Rh positive
– Reacting from 1+ to 3+ or greater
HOWEVER, some D-positive rbc’s DO NOT react (do NOT
agglutinate) at Immediate Spin using Reagent Anti-D.
These require further testing (37oC and/or AHG) to determine
the D status of the patient.
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Cross-matching involves mixing a sample of the
recipient's serum with a sample of the donor's red blood
cells and checking if the mixture agglutinates ,or forms
clumps.
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If agglutination is not obvious by direct vision, blood
bank technicians usually check for agglutination with a
microscope .If agglutination occurs, that particular
donor's blood cannot be transfused to that particular
recipient .
Blood group test
Sample is fresh blood or EDTA blood (anticoagulant)
Put 10 µ of anti A on one side of a slide and put 10 µ of anti
B on the other side
Put 10 µ of blood tested in each side and mix the blood with
the reagent added.
results:
+A & + B = AB
+A & - B = A
-A&+B=B
-A & - B = O