ABO 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 antigens Biochemical & Genetic Considerations

ABO and H Genetics ABO and H Antigen 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 Precursors Type I and Type II 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 Fucose Galactose

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 allele 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.

Group OGroup 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 A A Group OGroup A

Other ABO conditions Bombay Phenotype (O h ) 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 AB O44 Anti-A,B

ABO 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 HDNB Yes Transfusion Reactions ExtravascularIntravascular Yes

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 Positive Rh 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 Abs Clinically Significant Yes Abs class IgG Thermal range 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 Placenta Rh + 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 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 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