Introduction to ABO Blood Groups

Dr. Hemalatha Shanmugam

Department of Pathology

University Malaya

Learning objectives

Basic ABO/Rh blood group systems

Basic pretransfusion compatibility testing

Blood groups The International Society of Blood Transfusion (ISBT)

currently recognizes 30 major blood group systems and more than 300 blood group antigens

In addition to the ABO and Rh antigens, many other antigens are expressed on the red blood cell surface

Blood groups Eg. an individual can be AB RhD positive, and at the

same time M and N positive (MNS system), K positive (Kell system), and Lea or Lebpositive (Lewis system)

ABO blood group system Discovered in 1901 by Karl Landsteiner

Present on the surface of red blood cells as well as tissue and endothelial cells in the body

Also found in soluble form in plasma and other secretions

ABO blood group system Inherited in simple Mendelian fashion

ABO genes are three in number (A, B or O) and found on chromosome 9

A and B genes produce a detectable product whereas O gene (amorph) does not produce a detectable product

ABO blood group system Each person will have a pair of genes eg. AA, AO, AB,

BB, BO, OO

Blood group Gene combinations

A AA or AO

B BB or BO

AB AB

O OO

ABO antigens The H antigen is an essential precursor to the ABO

blood group antigens and consists of a chain of D-galactose, N-acetyl-glucosamine, D-galactose and α-L-fucose, the chain being attached to the protein

H locus is located on chromosome 19 and it encodes a fucosyltransferase that produces the H antigen on RBCs

ABO antigens

ABO antigens • A and B genes do not directly produce antigens

• They code for an enzyme called a transferase

The A allele encodes a glycosyltransferase that bonds α-N-acetylgalactosamine to D-galactose end of H antigen, producing the A antigen

The B allele encodes a glycosyltransferase that joins α-D-galactose bonded to D-galactose end of H antigen, creating the B antigen.

ABO antibodies ABO blood group system is the ONLY blood group

system where the person produces antibodies corresponding to antigens not present on the surface of red cells

Natural antibodies

However, some exposure to antigens must take place for antibody production to occur

ABO antibodies • It is possible that food and environmental antigens

(bacterial, viral, or plant antigens) have epitopes similar enough to A and B glycoprotein antigens

• Anti-B antibodies are hypothesized to originate from antibodies produced against Gram-negative bacteria, such as E. coli

ABO antibodies Newborns have no detectable antibodies

Antibodies start forming at 4-6 months of age and levels reach adult levels at 5 years of age

Antibody levels may reduce with advancing age

ABO antibodies Generally IgM but small amounts of IgG also present

Can activate complement effectively and lead to intravascular haemolysis

Clinically significant

Anti-A, anti-B, anti-A,B

Generally do not cross the placenta

ABO grouping Forward grouping using known antisera to detect

presence of ABO antigens

Reverse grouping using known red cells to detect the presence of anti-AB antibodies

Methods: tile method, tube method, gel card

Rh blood group Second most important blood group after ABO

Discovered in 1939 by Levine and Stetson

Highly polymorphic

ONLY found on red cells – no soluble forms

Integral lipoprotein

Rh blood group Inherited in a Mendelian fashion

Rh genes are found on chromosome 1 (C, c, D, E, e) and encode for 5 common Rh antigens

Inheritance of either 1 or 2 D genes will designate the person as Rh positive

When no D gene is inherited from either parent, an individual will be designated as Rh negative

Rh Blood group All recipients and blood donors are routinely tested for

presence or absence of D antigen

If Rh negative, full Rh genotyping will be done

99% of Malaysian blood donors are Rh positive as compared to Caucasions (85%)

Rh blood group

Rh blood group Inheritance for Cc and Ee are also in Mendelian

fashion

Each parent will contribute either E or e and either C or c

Possible combinations: CCEE, CcEe, ccee

Rh Blood group Clinical significance:

Highly immunogenic and capable of forming antibodies in antigen negative individuals

Haemolytic transfusion reactions

Haemolytic disease of the newborn

Rh antibodies Majority are of IgG type

Not effective in activating complement

Can cross the placenta

Clinically significant

Not naturally occurring – produced after exposure to antigen positive blood eg. transfusion or pregnancy

Pretransfusion testing The purpose of pretransfusion or compatibility testing

is to minimize the risk of blood transfusion to a patient by selecting blood and blood components that will have acceptable survival when transfused and will not cause destruction of the recipients red cells.

Pre-transfusion testing 1. Review of recipients past blood bank history and

records

2. ABO and Rh type of both donor and recipient

3. Screening of recipients sera for unexpected antibodies

4. Crossmatch

Collection, Identification and Storage of Patient Sample 1. Identification of recipient

2. Proper labelling of blood tubes

3. Name, Age, Date of Birth, l.D.No. and Date

4. Nature of specimen * EDTA * Sample should not be haemolysed * Sample should be less than 3 days old

Cont.. 5. Test on Neonate

Baby’s blood specimen for ABO & Rh(D) grouping

Mother’s serum for crossmatching

6. Identification of blood sample in the blood transfusion laboratory

Name in the form and tube match

Sample inspection

Cont.. 7. Request Form

Transfusion request form must contain sufficient information for definite identification of the recipient. It should include: - Name - Age/Date of birth - Sex - Registration number (1.D.No.) - Ward/Bed No. - Address

Cont.. The blood sample alone with the request form should be

signed by a doctor or a phelebotomist collecting the sample.

Laboratory personnel should check the information on the request form with the sample and record the time of receiving the request form.

Review of recipients past blood bank history and records Checking previous transfusion records

ABO & Rh(D) group

presence of unexpected antibodies

any problem in compatibility testing

previous transfusion reaction

any transfusion

ABO and Rh type of both donor and recipient Perform ABO and Rh(D) grouping using a recommended

technique

Any discrepancy must be resolved before blood is issued

In emergency situations, emergency O red cells can be issued until the discrepancy is resolved

If problem with Rh (D) typing, give Rh (D) negative blood.

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