Allergic and anaphylactic transfusion reactions

Overview

•Symptoms begin within minutes of starting transfusion (sometimes after only a few millilitres)

•Anaphylaxis: urticaria, angioedema, bronchospasm/wheeze, hypotension, tachycardia - typically NO fever or haemoglobinuria

•Mild allergic reaction: urticaria only, haemodynamically stable

⚠️

Fever + haemoglobinuria + back/flank pain + hypotension = acute haemolytic reaction, NOT anaphylaxis. Abdominal/chest/loin pain during transfusion also points to acute haemolytic reaction. These require fundamentally different management.

Investigations

•Treatment must not wait for results in anaphylaxis - investigations are post-stabilisation

•Serum tryptase - sample at 1-2 hours post-reaction + convalescent at 24 hours; raised level confirms anaphylaxis

•Serum IgA level - check after any moderate-to-severe allergic reaction; IgA deficiency (~1 in 600-700) with anti-IgA antibodies causes severe anaphylactoid reactions

•Anti-IgA antibodies - if IgA level low

•Repeat group and save + DAT - to exclude concurrent haemolytic reaction

Management

•First step: stop the transfusion immediately

•First-line (anaphylaxis): adrenaline 500 micrograms IM into thigh - given before antihistamines or steroids

•Supportive: high-flow oxygen + IV fluid bolus (500 mL 0.9% sodium chloride)

•Adjuncts: chlorphenamine 10 mg IV + hydrocortisone 200 mg IV

•Mild urticarial reaction only: may give chlorphenamine and observe; transfusion may be cautiously restarted if symptoms resolve

⚠️

IV adrenaline carries significant risk of fatal arrhythmia - only used by experienced clinicians in refractory, monitored settings. IM into the thigh is safer and achieves reliable plasma levels.

Differentiating transfusion reactions

Prevention and follow-up

•Repeated allergic reactions: pre-treat with chlorphenamine before future transfusions

•Confirmed IgA deficiency with anti-IgA antibodies: all future components must be IgA-depleted or from IgA-deficient donors - arranged via blood transfusion service

•All moderate/severe reactions: report to blood bank and file a SHOT (Serious Hazards of Transfusion) report; return implicated unit to laboratory

•Refer confirmed IgA-deficient patients to immunology/allergy before further transfusion