Blood Grouping & Compatibility

Question 1

What is blood grouping dependent on?

Answer 1

depends upon antibody-antigen interactions

Question 2

Describe Monoclonal Antisera

Answer 2

• monoclonal antibodies exhibit high degrees of potency, avidity & specificity
• Anti-A reagent is dyed blue
• Anti-B is dyed yellow
• manufactured & standardised

Question 3

Describe Reverse Typing

Answer 3

• if there is only a sample of plasma or serum:
• mix plasma/serum with a known red cell type
• group A plasma will contains an anti-B antibody that will agglutinate group B red cells

Question 4

What are some problems with agglutinations?

Answer 4

• clots -> small clots could be misread
• Rouleaux -> associated with older samples or disease states - can easily be dispersed using saline

Question 4

What are some variants of the D-antigen ?

Answer 4

• Partial D -> the Rh(D) compromises of 30 epitopes, rarely some individual are lacking certain epitopes.
• Weak D -> weak expression of the surface antigens - can be typed as Rh(D) negative

Question 5

What is the point of compatibility testing?

Answer 5

needs to test potential interaction between donor red cells & recipient’s serum

Question 6

Why is compatibility testing important?

Answer 6

• if patient has had previous transfusion may have raised IgG antibodies against certain Rh antigen
• may spontaneously develop cold reacting antibodies
• or be undergoing an immune haemolytic reaction

Question 7

Describe an Indirect Antiglobulin test

Answer 7

1. recipients serum is obtained containing antibodies
2. Donor’s blood sample is added to the tube with serum
3. recipient’s Ig that target donor’s red blood cells form antibody-antigen complexes
4. anti-human Ig’s are added to the solution
5. Agglutination of red blood cells occurs, because human Ig’s are attached to red blood cells

Question 8

What is AHG?

Answer 8

• Anti Human globulin - is a polyspecific reagent that contains an antihuman polyclonal IgG- raised in animals
• also contains a monoclonal anti-C3d

Question 9

Describe a Direct Coombs test

Answer 9

1. sensitised individual possibly following a transfusion reaction
2. confirms that red cells were under immune attack in circulation

Question 10

Describe an Antibody Screen

Answer 10

• when a positive screen is obtained, the specificity is determined by reacting the serum/plasma against a panel of red cells of known phenotypes

Question 11

Describe an immediate spin crossmatch

Answer 11

• Donor red cells suspended in saline are incubated with patient’s plasma for 2-5 minutes, then centrifuged + examined for agglutination
• designed to detect only ABO incompatibilty
• may get false negatives if Ab titres are low
• may get false postives from rouleaux or cold reacting antibodies

Question 12

What are some benefits of electronic issue?

Answer 12

• reduced manual workload
• rapid availabilty of blood
• improved stock control
• less exposure to bio-hazardous material
• proven to be safe if all essential criteria are met