T1 - Introduction to Transfusion Science

Question 1

Applications of Transfusion Science

Answer 1

Identification of antigens and antibodies
Selecting compatible blood for transfusion
Paternity testing
Transplantation

Question 2

What is a blood group?

Answer 2

One or more red blood cell surface antigens controlled by an allelic gene
- allelic gene is a gene whose variance is caused by a mutation in a specific locus

Question 3

ISBT Blood Group Requirements

Answer 3

The antigen must be inherited
The gene encoding it must have been identified and sequenced, and its chromosomal location known
The gene must be different from all other genes encoding antigens of existing blood group systems
The corresponding human alloantibody must be identified

Question 4

RBC Antigens

Answer 4

Complex protein or carbohydrate structures on/in the RBC membrane
Antigens in the same blood group (usually) arise from single nucleotide polymorphisms (SNPs) encoding an amino acid substitution in:
1. The antigen itself (protein)
2. A glycosylaminotransferase enzyme (CHO)

Question 5

Roles of Blood Group Antigens

Answer 5

Transporters or channels
Receptors for exogenous ligands, viruses, bacteria and parasites
Adhesion molecules
Enzymes
Structural proteins
Others

Question 6

RBC Antibodies

Answer 6

Antibodies directed against RBC antigens can develop in response to contact with ‘foreign’ antigens (on RBCs or in the environment)
Two groups of RBC antibodies
- naturally occurring
- immune

Question 7

Naturally Occuring Antibodies

Answer 7

Present in plasma without any known immunisation
Not present at birth
Ig subtype: IgM
React optimally at 4°C
'Complete'
Examples:
- anti-A
- anti-B
- anti-Lewis
- anti-M
- anti-N

Question 8

Immune Antibodies

Answer 8

No cross reaction between antigenic structure on naturally occurring substance and antigens on RBCs
Produced following:
- a blood transfusion
- immunisation during pregnancy
- intentional immunisation (exception: as an auto-immune antibody in certain diseases)
Ig subtype - IgG
React optimally at 37°C
'Incomplete'
Examples:
- anti-Rh
- anti-Kell
- anti-Duffy
- anti-Kidd

Question 9

RBC Antigen/Antibody Binding

Answer 9

An antibody can bind to a RBC antigen in vivo or in vitro
In vivo, it results in intravascular or extravascular haemolysis, which is bad
- haemolytic transfusion reaction (HTR)
- haemolytic disease of the newborn (HDNB)
RBC is damaged via
- complement activation
- antibody-dependent cell-mediated cytotoxicity (ADCC)
In vitro, RBC antigen/antibody binding can be used to:
- determine an individual’s blood group
- determine if donor blood is compatible with that of the recipient
- identify antibodies present in patient plasma
- determine if an individual’s RBCs are coated with antibody

Question 10

Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)

Answer 10

Antibody-coated RBC binds to macrophage via Fc receptor
IgG mediated
Results in extravascular haemolysis

Question 11

Haemagglutination

Answer 11

Occurs in two stages:
1. Sensitisation
2. Agglutination
Haemagglutination stages with IgM antibody:
1. Sensitisation - antibody binds to cells
2. Agglutination - bound antibody cross-links cells
Haemagglutination stages with IgG antibody:
1. Sensitisation - antibody binds to cells
2. Agglutination - add anti-IgG to cross-link cells

Question 12

Factors Affecting Haemagglutination

Answer 12

Centrifugation
pH
Temperature
- 4°C vs RT vs 37°C
Ionic strength of buffer
Antigen/antibody ratio
- correct concentration of RBCs for the detection technique

Question 13

Haemagglutination Detection Methods - Tube

Answer 13

Add 1-2 drops of plasma or reagent to test tube
Add 1 drop of 3% RBC suspension to the same tube
Centrifuge
Read (grade) result

Question 14

Grading Tube Reactions

Answer 14

0 - no agglutinates, leave bottom of tube easily
1+ - small agglutinates with reddish background
2+ - many medium sized agglutinates
3+ - one or two large agglutinates, some smaller agglutinates
4+ - one large cell agglutinate