Blood Group Antigens and Antibodies

Question 1

What can stimulate Antibody production against Blood group Antigens?

What does the Transfusion of incompatible blood lead to? What increases the likelihood of this happening?

What can Antibody-Antigen reactions in the Body lead to?

What is Agglutination?
→ What can this be used to test the presence of?

Answer 1

• Blood transfusion, Pregnancy (foetal antigens entering maternal circulation), and Environmental factors
• Antibody production - Likelihood increases with more transfusions
• Cell death Directly in the blood (Intravascular Haemolysis) OR, Indirectly, the liver and spleen can remove the antibody-coated cells (Extravascular)
• Clumping of RBCs into visible agglutinates by antibody-antigen reactions
  → • RBC antigen - For blood grouping
  • Antibody in the plasma - For screening/identification

Question 2

ABO GROUPING SYSTEM:
What are the A, B and O Alleles?

1. Group A - What Antigens do they have? What’s the Genotype? What Antibodies do they have?
2. Group B - What Antigens do they have? What’s the Genotype? What Antibodies do they have?
3. Group AB - What Antigens do they have? What’s the Genotype? What Antibodies do they have?
4. Group O - What Antigens do they have? What’s the Genotype? What Antibodies do they have?

How can the Patient’s RBC’s be tested? What does a Positive result show?

How can the Patient’s Plasma be tested? What does a Positive result show?

Which Group can receive any type of Blood?

Which Group can give Blood to anyone?

Answer 2

• • A and B alleles are DOMINANT
  • O allele is RECESSIVE

1. A antigens, AA or Ao genotype, Anti-B
2. B antigens, BB or Bo genotype, Anti-A
3. A and B antigens, AB genotype, No antibodies
4. No antigens, oo genotype, Anti-A and Anti-B

• Mixed with Anti-A, Anti-B or Anti-D
  o Agglutination shows that a particular antigen is present on the RBC
• Mixed with A or B cells
  o Agglutination shows that a particular antibody is present in the plasma
• Group AB
• Group O

Question 3

RHESUS GROUPING SYSTEM:
What is the RhD Allele?

Why can transfusion of the D antigen cause very severe reactions?

Haemolytic Disease of the Newborn (HDN):
What are the 3 steps that occur here?

What events can cause Foetal blood to enter the Mother’s circulation?

To find those at risk of HDN, when are Blood group and Antibody screens carried out during the pregnancy?
→ What can be given to the at-risk D- mother?

Answer 3

• DOMINANT
• D antigen is very immunogenic, so Anti-D is easily produced
• Haemolytic Disease of the Newborn (HDN)
• 1. D- mother is carrying a D+ foetus. D antigens from foetus can enter the mother’s blood.
     
     2. Mother produces Anti-D
     3. If pregnant with another D+ foetus, the Anti-D will cross the placenta and kill the foetal RBCs
• Abdominal trauma, Intrauterine death, Abortion/Miscarriage
• At Booking and Week 28
  → Anti-D Prophylaxis (prevents full immune response against D antigen)

Question 4

Indirect Anti-globulin Test (IAT):
What is it used to detect?

What is Zeta Potential of the RBCs?
→ Why can IgM bind both RBCs but IgG can’t?

Cross-matching:
What does it test for?

If the Antibody screen is Negative, what can be carried out?

If the Antibody screen is Positive, what can be carried out?

What will a Positive Cross-match test present with?

Answer 4

• IgG
• RBCs have a positively charged ion cloud around them that prevents them from getting close to one another
  → IgM is large enough, but IgG is too small
• LISS added to counteract this Zeta potential, so agglutination to occur
• Compatability of donor and recipient blood
• Immediate Spin Cross-match (ISX) to check the donor’s RBCs against the recipient’s plasma
• IAT Cross-match
• NO AGGLUTINATION