MC

• Rh Blood Group System


  A human blood group system, the second most important after ABO in the cross-match test, discovered in 1940 after work on Rhesus monkeys
• Rh Blood Group System

  • The most complex system with over 45 antigens
  • The genes that control the system are autosomal dominant located on the short arm of chromosome 1
• Rh Antigens


  Proteins on the red blood cell membrane

  
• Most important Rh antigens

  • D
  • C
  • c
  • E
  • e
• RhD gene


  Encodes the D antigen, which is a large protein on the red blood cell membrane and is the most important

  
• RHCE gene


  Codes for Ce, cE, ce or CE polypeptides

  
• Frequency of D antigen

  85% (Rh positive), while the ABSENCE of the D antigen is 15% (Rh negative)

  
• Rh


  Refers to the presence or absence of the D antigen on the red blood cell
• Unlike ABO antigens, Rh antigens are present only on red blood cells and not on other blood cells including platelets and leukocytes
• D antigen


  Highly immunogenic
• 0.1 mL D+ blood can cause anti-D production in 50-70% of Rh(D) negative people who are exposed to the D antigen
• Rh antigens Immunogenicity


  • D > c > E > C > e
• Nomenclature of the RH system

  • Fisher-Race
  • Weiner
  • Rosenfield
• Fisher-Race Theory


  Rh inheritance is controlled by 3 closely linked loci on each chromosome of a homologous pair, each locus has its own set of alleles that are: Dd, Cc, and Ee. There is NO d antigen or allele, little d indicates the ABSENCE of the D antigen and nothing more.
• Weiner Theory


  There is one Rh locus at which occurs one Rh gene, but this gene has multiple alleles. The main difference is that the Fisher-Race theory has three closely linked loci, while the Weiner theory has only one gene locus at which multiple alleles occur.
• Rosenfield Nomenclature


  Each antigen assigned a number: Rh 1 = D, Rh 2 = C, Rh 3 = E, Rh 4 = c, Rh 5 = e.
• Significance of Rh system

  • After ABO, the Rh system is the second most important system because the D antigen is extremely immunogenic
  • Antibodies to Rh antigens can be involved in hemolytic transfusion reactions and anti-D is the most common cause of severe hemolytic disease in newborns (HDN) and can cause in-utero death
• Rh (+ve) type


  Can give to (+ve) type only; and receives from both (+ve, -ve) types
• Rh (-ve) type


  Can give to both (+ve, -ve) types, but receives from (-ve) type only
• The C and E antigens are not as immunogenic as D, routine typing for these antigens is not performed
• Weak D (Du) Phenotype

  1. positive RBC's that do not react (do not agglutinate) at immediate spin using reagent anti-D, require further testing (37C° and/or AHG) to determine the D status of the patient
• Mechanisms that account for the Weak D antigen

  • Du Variant (Partial D)
  • Hereditary Du (Genetically Transmissible) (weak D)
  • Position Effect (Gene Interaction Effect)
• Rh null


  An individual that appears to have no Rh antigens, no D, C, c, E, e antigens are present on the RBC membrane, RBC has a fragile membrane - is short-lived, demonstrates mild hemolytic anaemia, stomatocytosis
• Rh Antibodies


  Result from the exposure to Rh antigens, are IgG form and bind at 37°C, cause intravascular hemolysis (hemolytic transfusion reactions, HDN)

  
• Clinical Significance of Rh Antibodies


  • Hemolytic transfusion reactions: Re-exposure to antigen causes a rapid secondary response
  • Hemolytic disease of newborn (HDN): if the mother is Rh negative and the fetus or baby is Rh positive, the antibody can cross the placenta and destroy Rh (D) positive fetal cells resulting in death
• Blood Banking


  The process of collecting and preparing whole blood or blood products for transfusion, as well as the selection of appropriate, compatible blood components for transfusion

  
• Blood Bank Laboratory


  • The main and major role is to provide the safest and most compatible blood or blood components to all recipients
  • Blood banking includes typing the blood for transfusion and testing for infectious diseases

  
• Blood Bank Antigens


  RBCs possess antigens on their surfaces that have blood group specificities, hundreds of red cell antigens are recognized nowadays, but few are considered in the blood bank

  
• Antibodies

  Proteins produced by lymphocytes as a result of stimulation by an antigen which can then interact specifically with that particular antigen
• Classes of Antibodies

  • IgM
  • IgG
  • IgA
  • IgE
  • IgD

  
• Immunoglobulin


  Antibody formed as a result of immune stimulus (exposure to foreign antigen)
• Naturally occurring Antibody

  Antibody formed without prior exposure to foreign antigen
• Autoantibody

  Antibody formed to one's own antigens (abnormal condition)
• Alloantibody

  Antibody formed to foreign antigens, but within the same species
• Agglutinin


  Antibody capable of causing agglutination when reacting with the corresponding antigen
• Hemolysin


  Antibody capable of causing hemolysis when reacting with the corresponding antigen
• Cold antibody (cold agglutinin)

  Antibody whose optimal temperature of reactivity is less than 30 C
• Warm antibody

  Antibody whose optimal temperature of reactivity is greater than 35 C
• Stages of Antigen-Antibody Interaction

  1. Sensitization (coating of cells)

  2. Agglutination (cross-linkages between cells resulting in visible clumping)

  
• Factors Affecting Sensitization

  • Specificity
  • pH
  • Temperature
  • Incubation time