ABO Blood Group SystemABO Blood Group System

Importance of 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– This means that incompatibilities can cause life threatening

situations (transfusion reactions)

ABO antigensABO antigens

Biochemical & Genetic ConsiderationsBiochemical & Genetic Considerations

ABO and H ABO and H Antigen Genetics Genetics 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 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 Type I and Type II Precursors Precursors There are two potential precursors substances for ABH antigens

Type I and Type II

Both are comprised of identical sugars but the linkage of the terminal sugars differs in the two types

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.

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

Glucose

Galactose

N acetylglucosamine

Galactose

Precursor Substance (stays the

same)

RBC

Formation of the H antigen

Glucose

Galactose

N-acetylglucosamine

Galactose

H antigen

RBC

Fucose

H antigen 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 D-galactose to the terminal sugar of the H antigen “ 1-3 D-galactosyltransferase”.

Formation of the A antigen

Glucose

Galactose

N-acetylglucosamine

Galactose

RBC

Fucose N-acetylgalactosamine

Formation of the B antigen

Glucose

Galactose

N-acetylglucosamine

Galactose

RBC

FucoseGalactose

Genetics 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 alleleThe 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.

Group O Group A

Many H antigen sites

Most of the H antigen sites in a Group A individual have been

converted to the A antigen

Fewer H antigen

sites

A

A A

AA

Group O Group A

Other ABO conditions

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 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

– 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 PhenotypeFrequency(%) Serum Ab

A43Anti-B

B9Anti-A

AB4--------

O44 Anti-A,B

ABO antibody factsABO antibody facts• 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

ExtravascularIntravascular

YesYes

The Rhesus (Rh) Blood Group system

Rh Genetics: 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%

The presence or absence of D Ag determines if the person is Rh+ or Rh-

Rh PositiveRh Positive

Rh NegativeRh Negative

Rh Deleted : 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– No D, C, c, E, e antigens present on the RBC membrane

Rh antibodies

Rh AbsClinically Significant

Yes

Abs class

IgG

Thermal range

4 - 37

HDNB

Yes

Transfusion Reactions

ExtravascularIntravascular

YesNo

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.

Hemolytic disease of the Newborn (HDN)

Rh factor can cause complications in some pregnancies.

Mother is exposed to Rh antigens at the birth of her Rh+ baby.

First pregnancy

PlacentaRh+ antigens

Rh factor

Anti-Rh+ antibodies

Possible subsequent pregnancies

Mother makes anti-Rh+ antibodies.

During the mother’s next pregnancy, Rh antibodies can cross the placenta and endanger the fetus.

Weak D PhenotypeWeak D Phenotype Most D positive RbC’s react macroscopically with Reagent anti-

D 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.

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.

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 testSample 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