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ABO Blood Group System

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

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ABO Blood Group System

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  1. ABO Blood Group System

  2. 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)

  3. ABO antigens Biochemical & Genetic Considerations

  4. 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 Hgene. • The presence or absence of the ABH antigens in secretions is indirectly controlled by the Se gene. • 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)

  5. 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

  6. Glucose Galactose Precursor Substance (stays the same) N acetylglucosamine Galactose RBC Precursor Structure RBC

  7. RBC Glucose H antigen Galactose N-acetylglucosamine Galactose Fucose Formation of the H antigen

  8. H antigen • The H antigen is the foundation upon which A and B antigens are built. • AandBgenes 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”.

  9. RBC Glucose Galactose N-acetylglucosamine Galactose N-acetylgalactosamine Fucose Formation of the A antigen

  10. RBC Glucose Galactose N-acetylglucosamine Galactose Galactose Fucose Formation of the B antigen

  11. 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 • 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.

  12. A A A A A Fewer H antigen sites Group O Group A 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

  13. 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

  14. 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

  15. ABO Antibodies

  16. ABO antibodies

  17. ABO antibody facts • Complement can be activated with ABO antibodies (mostly IgM, some IgG) • High titer: react strongly (4+)

  18. Rh Positive Rh Negative The Rhesus (Rh) Blood Group system • Rh Genetics: The genes that control the system are autosomalcodominant 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-

  19. 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

  20. Rh antibodies

  21. Hemolytic disease of the Newborn (HDN) • 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.

  22. Rh factor First pregnancy • Rh factor can cause complications in some pregnancies. Placenta Rh+ antigens • Mother is exposed to Rh antigens at the birth of her Rh+ baby.

  23. Mother makes anti-Rh+ antibodies. Possible subsequent pregnancies Anti-Rh+ antibodies • During the mother’s next pregnancy, Rh antibodies can cross the placenta and endanger the fetus.

  24. 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.

  25. 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 mixtureagglutinates, or forms clumps. • If agglutination is not obvious by direct vision, blood bank technicians usually check foragglutinationwith amicroscope. If agglutination occurs, that particular donor's blood cannot be transfused to that particular recipient.

  26. 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 sidePut 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

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