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Clinical investigations from the RACP

Investigating a patient with anaphylaxis

Richard M O’Brien

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Abstract

For most patients presenting with anaphylaxis, a confident diagnosis should be possible from the history and examination. In determining the cause, skin prick testing and serological testing are only occasionally helpful and can be misleading. Provocation testing is the most definitive method but is associated with significant risk.

Key Points

  • Anaphylaxis is an acute or rapidly evolving, systemic or multi-organ, life threatening reaction resulting from the release of mediators predominantly from mast cells and basophils.
  • For most patients presenting with anaphylaxis, a confident diagnosis should be possible from the history and examination.
  • If there is doubt about the diagnosis, the plasma tryptase level should be measured. Plasma tryptase is specific for anaphylaxis.
  • In determining the cause of anaphylaxis, skin prick testing is the standard method for detection of specific IgE, and is simple, quick and highly sensitive.
  • Serological testing for specific IgE is preferable to skin prick testing in selected cases – e.g. in patients with extensive skin disease, in those who are taking antihistamines or in those who are at risk of anaphylaxis.
  • Provocation testing is the most definitive method of determining the cause of allergic or nonallergic anaphylaxis but is associated with significant risk.

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