Alloimmunisation

This is a delayed (>24 hours), immunological transfusion reaction.
 

When to suspect this adverse reaction?

Clinical symptoms and signs may range from mild, including slight fever and a decreasing haemoglobin, to severe, with marked anaemia or platelet refractoriness with bleeding.(2)

The incidence rates for alloimmunisation associated with red cell antigens are 1 in 100 transfusions and with HLA antigens they are 1 in 10 transfusions.(1) 
 

Usual causes?

Alloimmunisation to red cells, white cells and/or platelets may result from prior exposure by the recipient to blood components, tissue transplantation or pregnancy. With the first exposure to foreign antigen a moderate amount of both IgG and IgM antibodies may be produced.(2)

However, upon a secondary exposure to this antigen, a rapid production of large amounts of IgG antibodies occurs in a few days which attach to the antigenic surface and can result in a delayed transfusion reaction.
 

Investigation

Obtain patient history of any previous transfusions, transplantations or pregnancies.

Perform an antibody screen tests on the patient’s plasma to detect clinically significant red cell antibodies or HLA antibodies.
 

What to do?

Treatment depends on the type and severity of the transfusion reaction with most reactions being mild.(2) Alloimmunisation cannot be completely prevented.

If an antibody is identified, you may request for antigen-negative blood if further transfusion is needed.

With patients on long term transfusion support, eg patients with thalassaemia, giving phenotyped blood early in their chronic support may reduce the risk of further antibody development.
 

References
  1. Roback JD (ed). Non-infectious complications of blood transfusion. Chapter 27, AABB Technical Manual, 17th edition. AABB, Bethesda, 2011.
  2. Harmening DM (ed). Chapter 18, Adverse Effects of Blood Transfusion. Modern Blood Banking and Transfusion Practices, 5th edition. FA Davis Company, Philadelphia, 2005.