ABO Blood Group System Flashcards
Landsteiner
Discovered ABO Blood Group
ABO Forward Group
Based on presence or absence of antigens A or B
- A - Group A
- B - Group B
- A & B - Group AB
- Neither A or B - Group O (aka Amorph)
ABO Forward Group
Only Blood group that has antibodies without antigen exposure
ABO Reserve Group
Based on antibodies in serum directed against antigens that person lacks
- Group A - Anti-B
- Group B - Anti-A
- Group AB has no antibodies
- Group O - Anti-A and Anti-B
ABO Reserve Group
Must correspond with opposite of forward group and is used to verify that the correct ABO has been identified
Landsteiner’s Rule
ABO System is the only blood group system in which the reciprocal antibodies (naturally occurring) are consistently and predictably present in the sera of normal people whose rbcs lack the corresponding antigens
Definition of Blood Group System
Includes those antigens that are produced by alleles at a single genetic locus
Percentage of ABO group in population
45% - Group O
41% - Group A
10% - Group B
4% - Group AB
RBC Membrane
Composed of glycosphingolipids
ABO antigens
Attach to the carbohydrate end of these molecules
Other Blood Group Systems
Antigens of P
Antigens of Lewis (reliant on ABH system)
Constructed on related carbohydrate molecules on RBCs
Glycosyl Transferases
A & B Genetic codes for production of enzymes
Oligosaccharides
Specific sugar added to end of the carbohydrate chains
Immunodominant Sugars
Sugar on end of carbohydrate chain determines ABO antigen
Genes for ABO Blood group
3 genes involved in Production of A and B antigens
ABO Gene
Chromosome 9
Hh Gene
Chromosome 19
Sese Gene
Chromosome 19
Hh Gene Info
H/h gene must act first
2 Alleles - H and h
H/H or H/h Genotypes
Code for fucosyltransferase
- adds fucose to CHO (carbohydrate) chain
- Produces H antigen
h/h Genotype
Very rare
Does not code for any antigen product
“Amorph”
Bombay phenotype
Fucose is NOT added to CHO (no structure to build A & B ag)
A & B Genes
Code for glycosyl transferase
O Gene
Does not code for any enzyme
A Gene Specific
N-acetylgalactosaminyl transferase
B Gene Specific
Galactosyl transferase
O Gene Specific
Adds no immunodominant sugar
H antigen remains on RBC
Bombay Phenotype
Testing mimics Group O person
Cells do not react with anti-A, anti-B, or anti-A,B
Serum contains anti A, anti-B, and anti-A,B
Serum also contains anti-H
Se Gene Effect on A & B expression
Responsible for expression of H, A, and B on glycoproteins in epithelial secretions
Se/Se and Se/se Genotype
Occur in 80% of population
- Type I Precursor Chains in secretions
- A, B, H antigens present in secretions
se/se Genotype
Occur in 20% of population
Amorph
No A, B, H antigens in secretions
H Gene Precursors
2 Types
- Type I - Body Fluids (1-3 linkage in sugars)
- Type II - RBC (1-4 linkage in sugars)
Embryo RBCs
Detected A & B antigen 5-6 weeks gestation
Antigens fully developed at 2-4 yrs
Phenotype
Set of observable characteristics based on genotype
Example: Child is Group A (could be AA or AO genotype)
Genotype
Genetic makeup
Example: Mom is Group O and Dad is Group AB
Child could be AO or BO (appear as A or B phenotype)
Immunocompetent
Produce antibodies to antigens they lack
IgM
Naturally occuring
IgG
Immune via exposure
Group A
Produces anti-B IgMG
Group B
Produces anti-A IgM
Group O
Produces anti-A, anti-B, and anti-A,B IgG
Antibody Production Begins
3-6 months of life
Newborn ABO
Does NOT include testing of serum (mother’s ab is in serum)
Antibody Production Decrease
Age
Immunosuppression
Subgroups of A
Affect amount of A antigen on RBCs
May cause typing discrepancies
Subgroups of B
Rare
Usually do not cause typing discrepancies
A1 and A2 Genes
Code for slightly different antigens
A2 - less antigen sites
80% of Group A are A1
20% of Group A are A2
Weaker subgroups of A
A3 and lower
Occur infrequently
Continued decreasing amounts of A antigen on RBCs
Increasing amount of H activity
A subgroups Antibodies
Naturally occurring anti-B
May produce an immune anti-A1
- Causes typing discrepancy
- 1-8% of A2 persons (IgM anti-B, IgG anti-A1)
- 22-35% of A2B persons
Forward Grouping
RBCs tested for presence of A and B antigens
Use reagent anti-A, anti B, and anti-A,B
Reverse Grouping
Serum is tested for presence of anti-A and anti-B antibodies
Reagent A1 (may need to use A2) and B cells
Clerical Discrepancies
Check names, numbers
Documentation
Tube/paperwork mixups
Technical Discrepancies
Cell suspension
SOP
Observations/interpretations
Centrifuges
Reagents/glassware
Weakly reacting Group 1
Due to age
Decreased immunoglobulins
- Disease
- Treatments
- Transplants
Weakly reacting Group 2
Due to subgroups
- Disease-related
- Acquired B antigen
- Antibodies to low incidence antigens
Proteins/plasma Group 3
Increased globulins
Increased fibrinogen
Presence of plasma expanders
Wharton’s Jelly - coating newborn cells causing spontaneous agglutination
Miscellaneous Group 4
Polyagglutination
Cold Reactive Antibodies
Warm Autoantibodies
Unexpected Antibodies in serum
Unexpected Ag-Ab complexes
cis AB phenotype
Resolution of ABO discrepancies
Check records and processing (Labeling and Patient history)
Serum-related (Type 1) or Cell-related (Type 2) Problem
Expanded (follow-up) Testing
- Repeat Testing
- Change Incubation Time/Temperature
- Special Reagents
- Other Procedures
