Haematology (AgAbscrID)

Question 1

What is an antigen?

Answer 1

Any substance capable of inducing a specific immune response and of reacting with the products of that response

Question 2

What is an antibody?

Answer 2

An immunoglobulin produced by the introduction of a foreign antigen

Question 3

What are the 2 mains ways that antibodies to other blood groups are produced?

Answer 3

Transfusion and preganacy

Question 4

How can haemolytic disease occur in newborns?

Answer 4

• Transplecental tears can cause foetus cells to leak into maternal circulation
• Blood group antigens inherited from father stimulate anti-antibody production in mother
• IgG’s small so can cross the placenta and bind to foetus blood antigens

Question 5

What is the name of such a disease? What does it cause?

Answer 5

Haemolytic Disease of the Foetus and Newborn (HDFN)

- causes neurological death and can lead to death

Question 6

What can occur in mild cases?

Answer 6

Baby born with anemia

Question 7

How can transfusion cause anti-antibody production?

Answer 7

• About 2% of patients produce unusual blood group antibodies to transfused RBCs
• Primary response may take up to 3 months for detectable antibody
• If subsequently transfused with RBC with corresponding antigens then these cells will be destroyed by immune system

Question 8

Over what 2 time frames can this transfusion reaction take place?

Answer 8

Immediate or delayed

Question 9

What are the range of symptoms in transfusion reactions?

Answer 9

From itching and hives through to death

Question 10

What are the 3 main ways to observe antigen/antibody reactions?

Answer 10

1) Agglutination

2) Haemolysis
- free haem turns plasma from straw colour to bright red

3) Inhibition

Question 11

What are the 2 phases of antigen/antibody reactions?

Answer 11

1) Sensitisation

2) Agglutinination (in vitro)

Question 12

What factors affect antibody/antigen reactions?

Answer 12

- Temperature
> IgM react well at room temp
> IgG temp dependant
- Incubation time
- Number of antigen sites
- Proximity of red cells
- Ionic strength of medium
- pH
- Antibody-antigen affinity
- Antibody-antigen concentration

Question 13

What is column agglutination technology (CAT)?

Answer 13

A system that uses the principle of density gradient seperation

A column of gel that is centrifuged to allow passage of unbound components but not aggluninates

Question 14

What are the 2 types of column agglutination?

Answer 14

1) Column contains antibodies and the patients red cells are passed through
2) Column contains reagent red cells (already phenotyped) and pass patients plasma though it (antibody screen)

Question 15

What is a positive reaction?

Answer 15

Agglunination between the red cell antigen and the antibody preventing it from passing through gel

Question 16

What is the Indirect antiglobulin test (IAT) used for?

Answer 16

Used to detect if there are clinically significant antibodies (excluding ABO) present

• IgG antibodies are too small to cause agglutinates due to RBC repulsion
• This technique allows agglutination

Question 17

What is a clinically significant antibody?

Answer 17

An antibody that binds to corresponding antigen in vivo, causing sensitisation
- Generally associated with shortened survival of transfused red cells or haemolytic disease of newborns/foetus

Question 18

How is the indirect antiglobin test (IAT) performed?

Answer 18

• Done at 37oC
• Donor red cells are mixed with serum/plasma of the patient, containing IgG antibodies
• Some cells will become sensitised with IgG if they bind to corresponding antigens
• Anti-Human Globbulin (AHG) is added to the IgG coated red cells
• AHG will bind multiple antibodies, causing Agglutination