Blood Typing

Blood typing is matching donated products to the donor, and is done to balance the:

A Brief Refresher on Blood Types:

• RBC may express either type A, type B, both, or no antigen
• The blood group refers to what antigen your RBC express
  The O blood group express no antigen on the RBC.
• Plasma contains IgM antibody to non-expressed antigens
  These are developed within 3-6 months of birth.
• Therefore, the following can be given to anyone with risk of ABO incompatibility:
  • Type O RBC, as they express no antigen
    Thus, type O are referred to as the universal donor.
  • Type AB plasma, as it contains no antibody
    Type AB have unjustly been referred to as the universal recipient, which is only true in an erythro-centric model of the universe.

• Risk of haemolytic transfusion reactions
• Urgency of required transfusion
• Allocation of scare resources

Blood products can be divided based on the degree of typing required:

• Untyped
  Immediately available. Use of untyped blood:
  • Consumes limited pool of universal units
  • Is justified in patients needing emergency transfusion
  • Is not justified in patients stable enough to wait until crossmatching is complete
  • Has a higher risk of transfusion reaction
    Risk is from minor antibodies.
    • Present in 2% of population
      Prevalence ↑ with age.
    • Typically IgG mediated
    • Does not generally cause major haemolysis
      Overall haemolysis rate of emergency transfusion is 0.1%.
  • For packed red cells is O-
    • Rh- (or unknown) females of childbearing age should receive O-
      Risk of rhesus disease if Rh+ blood given.
      • If prolonged/repeated transfusion required, use of Rh+ blood can be justified due to limited availability of Rh- blood
  • For plasma is usually AB+, but can be A+ with low anti-B
    Justified due to:
    • Very limited supply of AB+ plasma
    • Low risk of significant reactions in B patients receiving incompatible group A plasma:
      • Low overall presence of AB+ and B+ individuals
      • Dilution of recipient group B RBCs with untyped
      • Low risk of significant reaction in B patients

Each subsequent stage results in a significantly smaller ↓ in the absolute risk of incompatibility - the greatest gains are had with blood grouping and typing.

• Group-specific uncrossmatched
  
  • Prevents ABO reaction
  • 99.8% chance of compatibility
  • Rhesus-matching is mandatory in children and women of childbearing potential
    Prevent maternal antibody causing foetal haemolysis and subsequent miscarriage/death of an Rh+ foetus.
  • Generally available within 5-10 minutes
    
    
• Group-specific partial crossmatch
  • 99.94% chance of compatibility
    
    
• Group-specific fully crossmatched
  • 99.95% chance of compatibility
  • Generally available in 30-45 minutes

Typing Process

Testing a recipient and preparing donor blood for transfusion involves three stages:

1. Blood group (ABO and Rhesus) typing
   Takes ~15 minutes.
   • Forward gropuing
     Patient RBC mixed with anti-A and anti-B antibodies; agglutination indicates antigen presence.
   • Reverse grouping
     Patient plasma mixed with known type A or type B RBC; agglutination indicates antibody presence.
   • Forward and reverse grouping tests must agree to confirm an ABO grouping
     Divergence indicate:
     • Recent incompatible transfusion
     • Foetomaternal haemorrhage
     • Presence of a strange antibody.
   • Rhesus typing performed with known anti-D serum.
2. Antibody screen
   Screening for minor antibodies other than anti-A and anti-B.
3. Crossmatching
   Testing of patients blood with a particular donated sample to make sure they are compatible.
   • Detects:
     • ABO incompatibility
       Should be determined by the previous round of testing.
     • Minor antibody presence
   • Speed depends on the antibody screen:
     • A computer cross-match can typically match a unit of blood in <5 minutes, if the minor antibody screen is normal
     • An abnormal minor antibody screen requires a prolonged (usually manual) cross-match, which may take 45 minutes to several hours

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References

1. Bersten, A. D., & Handy, J. M. (2018). Oh’s Intensive Care Manual. Elsevier Gezondheidszorg.
2. Yazer MH, Waters JH, Spinella PC, et al. Use of Uncrossmatched Erythrocytes in Emergency Bleeding Situations. Anesthesiology. 2018;128(3):650-656.