Blood Groups

Master answer

Blood Typing

• The purpose of blood typing is the streamlining of blood products on the basis of the presence of antiogenetic surface membrane proteins in order to minimise patient harm.
• Main Types of Antigens:
  • ABO
  • Rhesus
  • Others:
    • Kell, P, MN, Lewis
    • less antigenic

ABO system:

Red blood cells possess genetically determined antigens on their cell membrane, termed
“agglutinogens”
Agglutinogens: glycoproteins, with differing terminal oligosaccharides

• H gene:
  • Forms “H-antigen” by addition of fructose to membrane glycoprotein
• A gene:
  • Forms “A-antigen” by extension of H-antigen with “N-acetyl-D-galactosamine”
• B gene:
  • Forms “B-antigen” by extension of H-antigen with “D-galactose”

Blood Groups:

Blood Group antibodies:

• Naturally-occurring Ab to A- and/or B-antigens (as anti-A and anti-B antibodies)
• IgM only
• Develop naturally after 3 months of age due to presence of Ag in bacteria/food that resemble A/B-Ag’s

Typing / Blood Group determination (Coombs)

• Red cells tested using anti-sera (Ab added to sample)
  • IgM anti-A and anti-B Abs added to sample
  • +ve agglutination indicates blood type
• “Reverse blood grouping” (Sample added to Ab)
  • Test individual’s serum using known group A, B, and O red cells
  • +ve agglutination indicates blood type

Antibody screen:

• Used to detect if an individual possesses antibodies other than those against agglutinogens A and B
• Individual’s blood is exposed to a number of red cells with known antigens, and if a reaction, an antibody is present
• A common antibody is the D antigen, or Rhesus factor
  • Highly antigenic
  • Present on RBC only
  • Three subtypes
    • Cc; Dd; Ee
    • d-Ag does not exist
  • Any combination of the three with a D-Ag is highly antigenic.
  • Rh +ve (if D-Ag present)

Cross Matching

Major Crossmatch: Test in vitro recipient’s serum and donor’s red cell
Minor Crossmatch: In vitro serological compatibility between donor’s serum and recipient’s red cells

Major Crossmatch:

1. Saline agglutination test
   • To reconfirm ABO grouping
   • It tests for presence of IgM (Eg. anti-A and anti-B Ab’s) in recipient serum against donor RBC
     • Donor’s RBCs + saline + recipient serum
     • +ve agglutination means incompatible ABO
2. Indirect Coomb’s test
   • To Reconfirm presence of “minor” Ab’s in recipient serum
   • Two stages:
     • Donor RBCs + recipient serum
       • RBC will be coated if Abs present
     • AHG test
       • RBC washed
       • “anti-human globulin” (AHG) added
       • agglutination
       • → recipient serum contains an Ab against donor RBC

Serological testing:

All donor blood is tested for:
HIV 1 + 2
Hepatitis B
Hepatitis C
HTLV-1

Mooney / Gladwin 2016

Answer by Gladwin, Mooney