ABO Anomalies

Question 1

ABO reverse group anomalies

Answer 1

1. Missing/weak antibodies
   
   • Age (newborn/elderly)
   • Immunocompromised e.g. hypogammaglobulinaemia
2. Extra antibodies
   
   • Cold autoantibodies e.g. Anti-I
   • Cold alloantibodies e.g. Anti-M
   • Rouleaux
   • Anti-A1

Question 2

How to resolve reverse group anomalies

Answer 2

Missing/weak antibodies = Incubate at 4C for 1hr + repeat.
Cold autoantibodies = incubate at room temp + repeat
Cold alloantibodies = Perform cold antibody panel.
Rouleaux = saline displacement technique
Anti-A1 = perform A2 typing with anti-A1 lectin

Question 3

Forward group anomalies

Answer 3

1. Missing/Weak antigens
   
   • A/B subgroups
   • Disease state e.g. leukaemia
2. Extra antigens
   
   • Acquired B antigen
   • B(A) phenotype
   • Rouleaux
3. Mixed Field
   
   • Blood Group O transfusion
   • Bone Marrow transplant

Question 4

Resolving forward group anomalies

Answer 4

1. A/B subgroups = use specific anti-sera e.g. Anti-A1 lectin reagent.
2. Disease state = = incubate at 4C to enhance reactivity
3. Acquired B antigen = check patient history for likely diseases (CRC), use anti-B reagent that does not react with acquired B antigens, test serum against patients own RBCs (should not react).
4. Rouleaux = saline displacement technique
5. Transfusion = check patient history and redo in a few weeks.

Question 5

What is B(A) phenotype?

Answer 5

Group B RBCs that express a low level of A antigens

Question 6

What is Acquired B antigens

Answer 6

Some bacteria can modify the structure of A antigens so that they mimic B antigens.
Associated with Gram negative bacteria e.g. E.coli
Associated with Colorectal cancer, lower GI tract infections.

Question 7

What is rouleaux

Answer 7

Clumping of RBCs due to increased levels of serum proteins.
Requires saline displacement to remove serum proteins and disperse the RBCs.

Question 8

Why does O blood group transfusion cause mixed field results

Answer 8

Transfusing O blood into A/B/AB+ individual.
In gel the A/B/AB+ RBCs will react with anti-sera but the O+ RBCs will not causing both a positive and negative result.

Question 9

Technical errors examples (5)

Answer 9

1. Sample collection from wrong patient
2. Labelling errors
3. Using expired/contaminated reagents
4. Uncalibrated centrifuge
5. Failure to add reagents/samples.

Question 10

Steps in investigating anomalous results

Answer 10

1. Repeat test using same sample to rule out technical errors (check reagents, centrifuge, pipetting technique)
2. Classify into reverse/forward group anomalies
3. Perform additional tests depending on suspected cause (Lectin testing, saline displacement, incubation).
4. Review patient history (age, medication or disease history, recent transfusion/transplants).
5. Repeat with fresh sample

Question 11

Example =
Cells are group A positive, RhD positive, anti-A and anti-B positive

Answer 11

Extra antibody in reverse group.
Anti-A1/ Rouleaux / cold antibodies
=> Subtype with anti-A1 lectin , perform cold panel, incubate at room temperature, saline displacement technique.