Anaphylaxis

Last reviewed: 23 Aug 2023

Last updated: 03 Nov 2020

Sudden onset of respiratory or cardiovascular compromise, usually with a history of allergen exposure in sensitized individuals.

Skin rash, wheezing and inspiratory stridor, hypotension, anxiety, nausea, and vomiting are the cardinal signs and symptoms.

The diagnosis is clinical. Allergy testing is helpful only for secondary prophylaxis.

Securing the airway and initiating prompt treatment with epinephrine (adrenaline) may save lives.

Comorbidities (e.g., coronary artery disease and COPD) may pose a treatment challenge and warrant expert consultation

Definition

Anaphylaxis is an acute, severe, life-threatening allergic reaction in presensitized individuals, leading to a systemic response caused by the release of immune and inflammatory mediators from basophils and mast cells. At least two organ systems are involved, such as the skin, the upper and lower airways, and the cardiovascular, neurologic, and gastrointestinal systems, in this order of priority or in combination. Allergy to medications, food, immunotherapy, or insect stings is the most frequent cause. Nonimmunologic anaphylaxis, previously described as an anaphylactoid reaction, produces similar symptoms.

History and exam

Key diagnostic factors

acute onset
urticaria
angioedema
flushing
dyspnea
wheezing
rhinitis

More key diagnostic factors

Other diagnostic factors

allergen ingestion
insect stings or bites
pruritus
inspiratory stridor and hoarse voice
bilateral conjunctivitis
nausea and vomiting
abdominal cramping or pain
agitation/anxiety
confusion/disorientation
tachycardia
dizziness
syncope
sense of impending doom (angor animi)
recent exercise
hot or cold exposure
hypotension
bradycardia
cardiac arrest
diarrhea
visual disturbances
tremor
seizures

Other diagnostic factors

Risk factors

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

More risk factors

Diagnostic investigations

1st investigations to order

serum tryptase level

More 1st investigations to order

Investigations to consider

in vitro IgE testing
skin test
challenge test

More investigations to consider

Emerging tests

basophil activation test

Treatment algorithm

INITIAL

all patients: acute onset

ONGOING

patients with identified allergen

Contributors

Authors

Doerthe Adriana Andreae, MD

Assistant Professor

Pediatric Allergy and Immunology

Penn State Health Milton S. Hershey Medical Center

Hershey

Disclosures

DAA is author of an UpToDate article on food allergy, for which she receives royalties. DAA is an author of a number of references cited in this topic.

Michael Henning Andreae, MD

Associate Professor

Department of Anesthesiology

Penn State Health Milton S. Hershey Medical Center

Hershey

Disclosures

MHA is an author of a reference cited in this topic.

Acknowledgements

Dr Doerthe Adriana Andreae and Dr Michael Henning Andreae would like to gratefully acknowledge Dr Andrea Vereda, a previous contributor to this topic.

Disclosures

AV declares that she is currently employed by Aimmune Therapeutics. AV wrote the main content of this topic before taking up this appointment.

Peer reviewers

Frank J. Domino, MD

Associate Professor

Family Medicine and Community Health

University of Massachusetts Medical School

Worcester

Disclosures

FJD declares that he has no competing interests.

Wayne Shreffler, MD, PhD

Assistant Professor of Pediatrics

Mount Sinai School of Medicine

New York

Disclosures

WS declares that he has no competing interests.

Lawrence Youlten, FRCP (Edin), PhD

Visiting Consultant in Allergy

Addenbrooke’s Hospital NHS Trust

Cambridge

Disclosures

LY declares that he has no competing interests.

Grant Hayman, MBChB, MRCP, DTM and H, MSc, FRCPath

Consultant Immunologist

Department of Immunology

Epsom & St Helier University Hospitals NHS Trust

Carshalton

Surrey

Disclosures

GH declares that he has no competing interests.

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Anaphylaxis

Summary

Definition

History and exam

Key diagnostic factors

Other diagnostic factors

Risk factors

Diagnostic investigations

1st investigations to order

Investigations to consider

Emerging tests

Treatment algorithm

all patients: acute onset

patients with identified allergen

Contributors

Authors

Doerthe Adriana Andreae, MD

Disclosures

Michael Henning Andreae, MD

Disclosures

Acknowledgements

Disclosures

Peer reviewers

Frank J. Domino, MD

Disclosures

Wayne Shreffler, MD, PhD

Disclosures

Lawrence Youlten, FRCP (Edin), PhD

Disclosures

Grant Hayman, MBChB, MRCP, DTM and H, MSc, FRCPath

Disclosures

Differentials

Guidelines

Patient leaflets

Videos

Log in or subscribe to access all of BMJ Best Practice

Log in or subscribe to access all of BMJ Best Practice

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