Anaphylaxis

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Last reviewed: 23 Apr 2025
Last updated: 11 Oct 2024

Summary

Definition

History and exam

Key diagnostic factors

  • acute onset
  • airway swelling (angio-oedema)
  • inspiratory stridor and hoarse voice
  • shortness of breath
  • wheezing, chest hyperinflation, and accessory muscle use
  • cyanosis
  • respiratory arrest
  • pale, clammy skin
  • hypotension
  • increased pulse rate (tachycardia)
  • bradycardia
  • cardiac arrest
  • confusion or disorientation
  • urticaria (hives)
  • erythema
  • pruritus
  • rhinitis
  • bilateral conjunctivitis
Full details

Other diagnostic factors

  • risk factors
  • nausea, vomiting, diarrhoea, and incontinence
  • abdominal cramps and pain
  • agitation, anxiety, and a sense of impending doom (angor animi)
Full details

Risk factors

  • adult age: food-, insect venom- and medicine-related
  • <30 years old: food-associated, exercise-induced
  • female sex
  • atopy/asthma
  • history of anaphylaxis
  • exposure to a common sensitiser (e.g., latex)
Full details

Diagnostic investigations

1st investigations to order

  • mast cell tryptase
  • 12-lead ECG
  • blood gases
  • urea and electrolytes
Full details

Investigations to consider

  • chest x-ray
Full details

Treatment algorithm

INITIAL

presumed anaphylaxis: in cardiorespiratory arrest

presumed anaphylaxis: not in cardiorespiratory arrest

ACUTE

after initial treatment: not in cardiorespiratory arrest

ONGOING

post-anaphylaxis

Contributors

Expert advisers

Alexander Alexiou, MB BS BSc DCH FRCEM Dip IMC RCSEd

Emergency Medicine Consultant

Barts Health NHS Trust

Physician Response Unit Consultant

London’s Air Ambulance

Royal London Hospital

London

UK

Disclosures

AA declares that he has no competing interests.

Thomas Palmer, BSc MBChB FRCEM

Emergency Medicine Consultant

Royal London Hospital

London

UK

Disclosures

TP declares that he has no competing interests.

Acknowledgements

BMJ Best Practice would like to gratefully acknowledge the previous team of expert contributors, whose work has been retained in parts of the content:

Doerthe Adriana Andreae MD

Assistant Professor

Pediatric Allergy and Immunology

Penn State Health Milton S. Hershey Medical Center

Hershey

PA

Michael Henning Andreae MD

Associate Professor

Department of Anesthesiology

Penn State Health Milton S. Hershey Medical Center

Hershey

PA

Disclosures

DAA is author of an UpToDate article on food allergy and a number of references cited in this topic. MHA is an author of a reference cited in this topic.

Peer reviewers

Robert Taylor, MBChB MRCP(UK) MRCP(London) DipMedTox DipTher PGDME FHEA FRCEM

Acute Hospital Sub Dean (Cornwall)

Honorary Clinical Senior Lecturer

Consultant Emergency Physician

The Knowledge Spa

Royal Cornwall Hospital

Truro

UK

Disclosures

RT declares that he has no competing interests.

References

Our in-house evidence and editorial teams collaborate with international expert contributors and peer reviewers to ensure that we provide access to the most clinically relevant information possible.

Key articles

Resuscitation Council (UK). Emergency treatment of anaphylactic reactions: guidelines for healthcare providers. May 2021 [internet publication].Full text

Cardona V, Ansotegui IJ, Ebisawa M, et al. World allergy organization anaphylaxis guidance 2020. World Allergy Organ J. 2020 Oct;13(10):100472.Full text  Abstract

National Institute for Health and Care Excellence. Anaphylaxis: assessment and referral after emergency treatment. August 2020 [internet publication].Full text

Muraro A, Worm M, Alviani C, et al. EAACI guidelines: anaphylaxis (2021 update). Allergy. 2022 Feb;77(2):357-77.Full text  Abstract

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.
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