Dr. Hemalatha Shanmugam Department of Pathology University Malaya
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.
THANK YOU