Transfusion medicine handbook

7. Adverse Effects of Transfusion

7.5 Allergic & Anaphylactic Reaction

Allergic reactions represent a spectrum of severity from mild, where the patient simply experiences isolated urticaria or a rash, through to fatal anaphylactic shock.

Allergic reaction

These are typified by one or more of the following: urticaria, rash, allergic dyspnoea (stridor, cyanosis, wheezing), localised angioedema or generalised pruritis without hypotension during or within 4 hours of transfusion. These reactions are commonly associated with transfusion of components with large volumes of plasma, for example platelets and FFP. Since the introduction of platelets suspended in platelet additive solution (PAS), the frequency of allergic reactions has reduced.

Symptoms usually subside if the transfusion is stopped and parenteral antihistamine is given. The transfusion may be continued if there is no progression of symptoms after 30 minutes.

A rise of mast cell tryptase can support the diagnosis of an allergic reaction.

Anaphylactic reaction

These are rare but life-threatening complications usually occurring during or very shortly after transfusion and are differentiated from mild/moderate allergic reactions by severity where, in addition to mucocutaneous features, there is airway compromise or severe hypotension requiring vasopressor treatment (or associated symptoms like hypotonia or syncope).

Anaphylaxis may occasionally be associated with antibodies against IgA in patients who have extremely low levels of IgA in their plasma or other genetic variants of plasma proteins. If this is the suspected cause the patient should, if possible, not be transfused. Special components will be needed in consultation with an NZBS Transfusion Medicine Specialist.

Premedication

Treatment with an antihistamine or hydrocortisone for generalised allergic reactions is justified. Premedication may be appropriate before transfusing a patient who has previously experienced repeated allergic reactions. Routine premedication with antihistamines prior to transfusion is however not advised, as it is both unnecessary and may modify important signs of a transfusion reaction.