Red cell antigens
The presence or absence of antigens on the surface of red cells allows laboratories to determine an individual’s blood group. The ABO and Rh blood group systems are the most well-known and the most significant in transfusion practice.
There are currently 43 different blood group systems that between them contain 345 red cell antigens.
Red cell antigens are not exclusively expressed on red cells and may be found on other blood cells and tissues.
How do we detect red cell antigens and antibodies?
Pretransfusion testing is performed to identify the patient's blood group and to detect pre-existing red cell antibodies. A Group and screen (or group and type) is performed to allow provision of compatible red cells. If a clinically significant antibody is detected, red cells that are negative for the relevant antigen must be crossmatched for transfusion.
Red cell antibodies
Antibodies are formed following exposure to foreign red cell antigens during transfusion or pregnancy. These IgG antibodies can cross the placenta and may cause haemolytic disease of the fetus and newborn.
The incidence of an immune red cell alloantibody is determined by the frequency of the antigen in the population and by its immunogenicity.
A patient may also have an antibody that reacts to all red cells irrespective of which antigens are present. This makes crossmatching difficult. These antibodies may also be associated with autoimmune diseases or medications.
Some newer monoclonal antibody treatments such as anti-CD38 (Daratumumab), used in the treatment of Multiple Myeloma, and anti-CD47 (Magrolimab) used in Myelodysplastic Syndrome (MDS), can interfere with pretransfusion testing. The extra testing to resolve this interference can delay the provision of blood so it’s important that the laboratory is made aware of the patient’s treatment so they can plan accordingly.