JPAC Joint United Kingdom (UK) Blood Transfusion and Tissue Transplantation Services Professional Advisory Committee

2.4: The ABO system

There are four main blood groups: A, B, AB and O. All normal individuals have antibodies to the A or B antigens that are not present on their own red cells (Table 2.1). The frequency of ABO groups varies in different ethnic populations and this must be taken into account when recruiting representative blood donor panels. For example, people of Asian origin have a higher frequency of group B than white Europeans. Individuals of blood group O are sometimes known as universal donors as their red cells have no A or B antigens. However, their plasma does contain anti-A and anti-B that, if present in high titre, has the potential to haemolyse the red cells of certain non-group O recipients (see below).

Table 2.1 Distribution of ABO blood groups and antibodies

Blood group

Antigens on red cells

Antibodies in plasma

UK blood donors

O

none

anti-A and anti-B

47%

A

A

anti-B

42%

B

B

anti-A

8%

AB

A and B

none

3%

 

2.4.1: Transfusion reactions due to ABO incompatibility

ABO-incompatible red cell transfusion is often fatal and its prevention is the most important step in clinical transfusion practice (Chapter 5). Anti-A and/or anti-B in the recipient’s plasma binds to the transfused cells and activates the complement pathway, leading to destruction of the transfused red cells (intravascular haemolysis) and the release of inflammatory cytokines that can cause shock, renal failure and disseminated intravascular coagulation (DIC). The accidental transfusion of ABO-incompatible blood is now classified as a ‘never event’ by the UK Departments of Health.

Transfusion of ABO-incompatible plasma containing anti-A or anti-B, usually from a group O donor, can cause haemolysis of the recipient’s red cells, especially in neonates and small infants. Red cells stored in saline, adenine, glucose and mannitol (SAG-M) additive solution (see Chapter 3) contain less than 20 mL of residual plasma so the risk of haemolytic reactions is very low. Group O red cell components for intrauterine transfusion, neonatal exchange transfusion or large-volume transfusion of infants are screened to exclude those with high-titre anti-A or anti-B. Group O plasma-rich blood components such as fresh frozen plasma (FFP) or platelet concentrates should not be given to patients of group A, B or AB if ABO-compatible components are readily available (Table 2.2). Cryoprecipitate contains very little immunoglobulin and has never been reported to cause significant haemolysis. In view of the importance of making AB plasma readily available, AB cryoprecipitate manufacture and availability is a low priority for the UK Blood Services.

Table 2.2 Choice of group of red cells, platelets, fresh frozen plasma (FFP) and cryoprecipitate according to recipient’s ABO group

Patient’s ABO group

Red cells

Plateletsa

Fresh frozen plasma (FFP)b

Cryoprecipitate

O

First choice

O

O

O

O

Second choice

 

A

A or B

A or B

Third choice

 

 

AB

 

A

First choice

A

A

A

A

Second choice

Oc

Od

AB

O or B

Third choice

 

 

Bd

 

B

First choice

B

Ad

B

B

Second choice

Oc

Od

AB

O or A

Third choice

 

 

Ad

 

AB

First choice

AB

Ad

AB

AB

Second choice

A or B

Od

Ad

A or B

Third choice

Oc

 

Bd

O

a Group B or AB platelets are not routinely available

b Group AB FFP is often in short supply

c Screening for high-titre anti-A and anti-B is not required if plasma-depleted group O red cells in SAG-M are used

d Tested and negative for high-titre anti-A and anti-B