HaematologyTier 1Disease (DEADMAN)

Allergic and anaphylactic transfusion reaction

Description

Hypersensitivity to a plasma protein in the transfused component
Spectrum: mild urticarial reaction (common) -> anaphylaxis (rare but life-threatening)
Different mechanism/severity spectrum, not simply "worse version" of the same reaction

Epidemiology

Urticarial reactions - relatively common (~1-3% of transfusions)
Anaphylactic reactions - rare (~1 in 20,000-50,000)
IgA deficiency with anti-IgA antibodies - classic (though rare) cause of severe/recurrent anaphylaxis, esp. with plasma-rich products

Aetiopathogenesis

Urticarial - IgE-mediated reaction to donor plasma proteins, usually mild, mast cell degranulation localised to skin
Anaphylactic - severe IgE (or non-IgE, e.g. complement-mediated) reaction
- IgA deficiency + anti-IgA antibodies - classic cause, reacts against donor IgA
- Other: haptoglobin deficiency, anti-C4 antibodies (rare)
Higher with plasma-rich components (FFP, platelets) than packed red cells

Diagnosis

Urticarial

Pruritus, urticaria/hives, flushing - no fever, no respiratory/haemodynamic compromise

Anaphylactic

Rapid onset (minutes) during transfusion: bronchospasm, stridor, hypotension, angioedema, GI symptoms - absent fever helps distinguish from haemolytic/septic reactions
Serum tryptase - supports diagnosis if measured acutely
Consider IgA level + anti-IgA antibody testing after the event if severe/recurrent

Management

Urticarial (mild, isolated)

Pause transfusion, give antihistamine, if resolves and no other symptoms may recommence cautiously and continue with slower rate/observation

Anaphylaxis

Stop transfusion immediately, do not restart
IM adrenaline first-line, standard anaphylaxis resuscitation (airway, oxygen, IV fluids)
Antihistamine, corticosteroid as adjuncts
Report as a transfusion reaction (haemovigilance) + notify blood bank

Prevention for future transfusions

Washed/plasma-reduced red cells or platelets - removes plasma proteins, reduces recurrence
If IgA deficient with anti-IgA - IgA-deficient donor products where available
Pre-medication (antihistamine) - reduces mild reactions but does not reliably prevent anaphylaxis

Associations

IgA deficiency (most classic association with severe anaphylaxis)
Atopy/prior allergic transfusion reactions - risk factor for recurrence
Plasma-rich products (FFP, platelets, cryoprecipitate) > packed red cells for risk

Natural history & complications

Urticarial reactions - self-limiting, do not preclude future transfusion
Anaphylaxis - can recur with subsequent transfusions if cause not identified/mitigated - document clearly and flag future transfusion orders
Rapid recognition and adrenaline administration is the key determinant of outcome

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