In this section
There are many blood groups in the human population including
ABO, Rh, Kidd, Kell, Duffy, MNS and Lewis. The most important of
these are ABO and RhD. Transfusion with ABO incompatible
blood can lead to severe and potentially fatal transfusion
reactions. RhD is highly immunogenic and can lead to red
cell haemolysis in certain settings.
The ABO blood group is the most important of all the blood group
systems. There are four different ABO blood groups (see
Table1), determined by whether or not an individual's red cells
carry the A antigen, the B antigen, both A and B antigens or
Normal healthy individuals, from early in childhood, make red
cell antibodies against A or B antigens that are not expressed
on their own cells. These naturally occurring antibodies are
mainly IgM immunoglobulins. They attack and rapidly destroy
red cells carrying the corresponding antigen. For example,
anti-A attacks red cells of Group A or AB. Anti-B attacks red
cells of Group B or AB.
ABO antibodies present
in the plasma
If ABO incompatible red cells are transfused, red cell
haemolysis can occur. For example if group A red cells
are infused into a recipient who is group O, the recipient's anti-A
antibodies bind to the transfused cells. An ABO incompatible
transfusion reaction may result in overwhelming haemostatic and
complement activation, resulting in shock, renal failure
& death (for more information please click here).
There are more than 40 different kinds of Rh antigens. The
most significant Rh antigen is RhD. When RhD is present
on the red cell surface, the red cells are called RhD
positive. Approximately 80% of the Australian population are
RhD positive. The remaining 20% of the population that lack
the RhD antigen are called RhD negative.
Antibodies to RhD develop only after an individual is
exposed to RhD antigens via transfusion, pregnancy or organ
transplantation. Anti RhD (or anti-D) antibodies destroy RhD
positive red cells and can lead to haemolytic transfusion
reactions. This is of particular importance in pregnancy
where anti-D antibodies can cross the placenta from mother to
unborn child and lead to haemolytic disease of the
As a general rule, RhD negative individuals should not be
transfused with RhD positive red cells, especially RhD
negative girls and women of childbearing age. If transfusion of an
RhD positive product to RhD negative recipient is unavoidable a
haematologist should be consulted and administration of anti-D
When a transfusion is given, it is preferable for patients
to receive blood and plasma of the same ABO and RhD
group. However if the required blood type is unavailable, a
patient may be given a product of an alternative but compatible
group as shown below.
Compatible Red Cell Types
Compatible Plasma Types
(FFP & Cryoprecipitate)
O, A, B, AB
AB, A, B, O
Note that Group O RhD negative (O negative) red cells have
neither ABO nor RhD antigens on their surface. O RhD negative red cells are issued in emergency situations where
life saving transfusion is required prior to completion of a
crossmatch. Both RCH and RWH blood banks maintain a
reserve of 5 emergency O RhD Negative red cells.
(Click here for
further information on emergency blood release). Group O
is often referred to as the universal red cell donor.
Group AB individuals have neither anti-A nor anti-B antibodies
in their plasma. Group AB plasma can therefore be given to
patients of any ABO blood group and is often referred to as the
universal plasma donor.
Most ABO incompatible transfusions occur as a result of
improper patient identification at the time of collection of the
pre-transfusion sample or administration of the blood
product. The pre-transfusion
check is carried out at the bedside by 2 members of
clinical staff to ensure the right blood is transfused to the right
patient. Positive patient identification prior to blood
sample collection and labelling the specimen tube at the bedside is
critical for accurate sample collection.
There are many other antigen systems expressed on red cells,
white cells and platelets. Transfusion can cause antibodies
to develop in the recipient. Some of these antibodies can
cause transfusion reactions or damage the foetus. The purpose
of pretransfusion testing (or crossmatching) is to detect potentially harmful
antibodies in a patient before transfusion and where possible
select red cell units that will not react with them.