For Patients & General Readers

Anaphylaxis is a sudden, severe, and potentially life-threatening allergic reaction. It can happen quickly after exposure to an allergen, such as certain foods, insect stings, or medications. Prompt recognition and treatment are crucial to prevent serious complications.

Clinical Overview

Anaphylaxis is a systemic, life-threatening hypersensitivity reaction caused by the rapid release of mediators from mast cells and basophils. It is characterized by acute onset of symptoms affecting multiple organ systems, typically involving the skin, respiratory, cardiovascular, and gastrointestinal tracts.

Clinical Presentation

Sudden onset of symptoms within minutes to hours after exposure to a known or suspected allergen.
Involvement of at least two organ systems (e.g., skin/mucosal, respiratory, cardiovascular, or gastrointestinal).
Hypotension or signs of hypoperfusion (e.g., syncope, collapse).
Progressive symptoms despite initial treatment.
History of previous anaphylactic reactions or known severe allergies.

Signs & Symptoms

Symptoms (Patient-Reported)

Itching or hives (urticaria)
Swelling of the lips, tongue, or throat (angioedema)
Difficulty breathing, wheezing, or shortness of breath
Chest tightness
Nausea, vomiting, diarrhea, or abdominal cramps
Dizziness, lightheadedness, or feeling faint
Sense of impending doom

Signs (Clinician-Observed)

Urticaria and/or angioedema
Bronchospasm (wheezing, stridor)
Hypotension (systolic BP < 90 mmHg or a significant drop from baseline)
Tachycardia
Cyanosis
Altered mental status

Differential Diagnoses

Condition	Distinguishing Feature
Vasovagal Syncope	Typically preceded by prodromal symptoms (nausea, pallor, sweating) and usually resolves spontaneously without hypotension or respiratory distress.
Asthma Exacerbation	Primarily respiratory symptoms without cutaneous or gastrointestinal involvement, and often a known history of asthma.
Sepsis	Gradual onset, often with fever and a clear source of infection; anaphylaxis is rapid and allergen-triggered.
Anxiety/Panic Attack	Can mimic some symptoms like shortness of breath and dizziness, but typically lacks objective signs of hypoperfusion or bronchospasm and is not triggered by allergen exposure.
Food Poisoning	Primarily gastrointestinal symptoms, often with a longer incubation period and without the rapid onset of systemic symptoms like respiratory distress or hypotension.
Mast Cell Activation Syndrome (MCAS)	Recurrent, unpredictable episodes of symptoms affecting multiple organ systems, but typically less acute and life-threatening than anaphylaxis, and often lacks a clear trigger.

Red Flags — Seek Immediate Care

Hypotension (systolic BP < 90 mmHg or significant drop)
Airway compromise (stridor, angioedema affecting the airway)
Respiratory distress (severe bronchospasm, hypoxia)
Loss of consciousness or altered mental status

Key Investigations

Clinical diagnosis based on history and physical examination.
Serum tryptase levels (elevated within 1-2 hours, peaks at 2-3 hours, and may remain elevated for 24 hours; useful for confirming anaphylaxis but not for immediate diagnosis).
Allergen-specific IgE testing (delayed, for identifying specific triggers after the acute event).
Pulmonary function tests (if not acutely ill, to assess for underlying reactive airway disease).

Management Overview

Immediate intramuscular administration of epinephrine is the cornerstone of anaphylaxis management. Supportive care includes airway management, oxygen, intravenous fluids for hypotension, and antihistamines and corticosteroids as adjunctive therapy. Patients should be monitored closely for at least 4-6 hours post-resolution and provided with an epinephrine auto-injector for future emergencies.

Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. TruelyserMD does not replace clinical judgement.