Severe allergic reactions

When to suspect this adverse reaction

Usually begin within a few seconds or minutes after the start of the transfusion. May be fatal.
Patients can present with a sudden onset of severe hypotension, cough, bronchospasm (respiratory distress and wheezing), laryngospasm, angioedema, urticaria, nausea, abdominal cramps, vomiting, diarrhoea, shock and/or loss of consciousness.
Occur in 1:20 adverse reactions.

Usual causes

The mechanisms below have been implicated in anaphylactic reactions:

  • IgA-deficient patients who have anti-IgA antibodies. Although IgA deficiency is not uncommon, fortunately most do not develop anti-IgA antibodies.
  • Patient antibodies to plasma proteins (such as IgG, albumin, haptoglobin, transferrin, C3, C4 or cytokines).
  • Transfusing an allergen to a sensitised patient (e.g. penicillin or nuts eaten by a donor). 
  • Rarely, the transfusion of donor IgE antibodies (to drugs, food, etc.) reacting with an allergen present in the recipient.


Anaphylaxis usually has a typical clinical presentation. Occasionally the clinical picture suggests a differential diagnosis of an acute haemolytic reaction, TRALI or TACO.
Direct antiglobulin test (DAT), full blood count and repeat ABO group may be indicated.

Check the recipient’s pretransfusion sample for IgA deficiency and presence of anti IgA antibodies if levels are very low.

What to do

Stop the transfusion immediately and follow other steps for managing suspected transfusion reactions. This may become a medical emergency.

Maintain an open airway and intravenous (IV) line, support blood pressure.
Administer supplemental oxygen, antihistamines, adrenaline and corticosteroids as required, resuscitation may also be necessary.

Consult a haematologist before administering additional blood components.

To prevent recurrent anaphylaxis consider the following options:

  • Perform further transfusions in a clinical area with resuscitation facilities.
  • Pre-medication with antihistamine.
  • Transfusion of washed red cells or platelets.
  • If the patient is IgA-deficient with anti-IgA, the use of IgA-deficient or washed blood components is recommended.
Acute Transfusion Reactions Card

Acute Transfusion Reactions Card

Information Sheet