Allergic reaction

Definition

Allergic reaction to plasma proteins in the donor unit (often against a specific donor); difficult to avoid and usually unpredictable.

Range from mild to severe (including anaphylaxis), with symptoms including flushing, urticaria or rash, wheeze, bronchospasm, stridor, angioedema and circulatory problems (not typically associated with fever type symptoms).

Frequency

Mild: Common (≥1 in 100 to <1 in 10).

Moderate and severe: Rare (≥1 in 10,000 to <1 in 1,000).

Reducing the risk

A small number of people may have recurrent allergic reaction to transfusion.

Measures to mitigate this include the use of:

• Platelets in additive solution
• Prophylactic antihistamine
• 'Washed' red cells
• Solvent-detergent treated plasma

Treatment as per local protocol (using antihistamine, adrenaline or steroids as indicated).

Further information and resources

Serious Hazards of Transfusion (SHOT) educational resources:

• SHOT Bite No.05a: Febrile, allergic and hypotensive reactions (FAHR) – Getting the diagnosis right
• SHOT Febrile, Allergic and Hypotensive Reactions Webinar 2020