Anaphylaxis occurs seconds to minutes after initiation of transfusion due to massive histamine release.  Symptoms include respiratory distress (eg, dyspnea, hypoxia), angioedema, and hypotension.  Wheezing is often appreciated, although decreased breath sounds can occur with severe bronchospasm preventing air entry.  Vomiting and urticaria may also be present.  Without treatment, symptoms can rapidly progress to respiratory failure and shock.

The first step in management is to immediately stop the transfusion and administer intramuscular epinephrine.  Bronchodilators and antihistamines are typically also administered.  In some cases, hemodynamic and respiratory support (eg, vasopressors, mechanical ventilation) may be required.

Patients with IgA deficiency are at higher risk of anaphylactic transfusion reaction because they may have anti-IgA antibodies that react with donor blood IgA and contribute to histamine release.  Although IgA deficiency can present with recurrent sinopulmonary infections, it is often asymptomatic and may be diagnosed only after an anaphylactic transfusion reaction.  Future transfusions should include IgA-deficient plasma and washed red blood cell products.

IgA levels are measured in patients with a suspected anaphylactic transfusion reaction, which typically presents within seconds to minutes of transfusion initiation.  Patients with this reaction have angioedema and respiratory distress.