In Canada, anaphylaxis is managed by allergy & immunologists. Anaphylaxis is a sudden, systemic, IgE-mediated (or non-IgE mast-cell-driven) hypersensitivity reaction that can kill within minutes by collapsing the airway and circulation simultaneously. Lifetime prevalence in the United States is approximately 1.6-5.1% across population surveys, with emergency-department visits rising roughly 5-fold over the past two decades.
Anaphylaxis (ICD-10: T78.2 anaphylactic shock, unspecified; T80.5 anaphylactic reaction due to serum) is a severe, life-threatening systemic hypersensitivity reaction defined by rapid onset and involvement of two or more organ systems, or hypotension or airway compromise after exposure to a known or probable allergen. Most episodes are immunoglobulin-E (IgE) mediated: an allergen cross-links specific IgE on the surface of tissue mast cells and circulating basophils, triggering release of histamine, tryptase, prostaglandin D2, leukotrienes, platelet-activating factor, and cytokines. The result is widespread vasodilation, increased vascular permeability, smooth-muscle contraction, and mucus hypersecretion across skin, airway, gut, and cardiovascular system. Non-IgE mechanisms (direct mast-cell activation, complement, MRGPRX2 receptor activation, contrast media) produce a clinically identical syndrome.
The key symptoms of Anaphylaxis are: Generalized urticaria (hives) or flushing that appears within minutes of exposure and spreads across the trunk and limbs — present in roughly 90% of anaphylactic episodes., Angioedema of the lips, tongue, uvula, or periorbital tissue that develops over minutes and may progress to upper-airway obstruction with stridor or muffled voice., Wheezing, chest tightness, shortness of breath, or audible inspiratory stridor reflecting bronchospasm and laryngeal edema — the most common cause of fatal anaphylaxis in food triggers., Hypotension, light-headedness, syncope, tachycardia, or collapse from massive vasodilation and fluid extravasation; systolic blood pressure under 90 mmHg in adults or under age-specific thresholds in children defines circulatory anaphylaxis., Sudden, crampy abdominal pain, nausea, vomiting, or explosive diarrhea within 30 minutes of exposure — gastrointestinal involvement appears in 30-45% of cases and is often missed., A sense of impending doom, anxiety, or behavioral change preceding objective signs, particularly described in adults; sudden quietness or limpness in infants and toddlers carries the same weight., Pruritus of the palms, soles, scalp, or genitals before any rash is visible — useful as an early warning sign especially in known allergic individuals..
Anaphylaxis is a clinical diagnosis made at the bedside; no laboratory test is required before treatment, and waiting for confirmation is dangerous. The 2006 NIAID/FAAN criteria (validated repeatedly and endorsed by the 2020 WAO update and 2023 ICON anaphylaxis paper) establish the diagnosis when any one of three scenarios applies. Scenario 1: acute onset of illness involving skin or mucosa plus either respiratory compromise or hypotension/end-organ dysfunction. Scenario 2: two or more of skin/mucosa, respiratory, cardiovascular, or persistent gastrointestinal involvement after exposure to a likely allergen. Scenario 3: hypotension alone after exposure to a known allergen for that patient. The criteria deliberately do not require all four systems; isolated severe respiratory or cardiovascular signs are sufficient. Serum total tryptase is the single most useful laboratory test: a mature tryptase rise of at least 1.2x baseline plus 2 ng/mL within 30 minutes to 4 hours of symptom onset supports the diagnosis (Schwartz 1989; Valent 2012). Tryptase must be drawn within 4 hours and a baseline value obtained at least 24 hours after recovery to interpret the delta. Tryptase is normal in 30-40% of food anaphylaxis (basophil-driven, low tryptase) and elevated in most venom and drug cases. After acute recovery, the workup transfers to an allergist for trigger identification: detailed exposure history, skin-prick testing, serum-specific IgE (ImmunoCAP), and where appropriate component-resolved diagnostics (Ara h 2 for peanut, omega-5 gliadin for wheat-dependent exercise-induced anaphylaxis, alpha-gal for delayed mammalian-meat reactions). Drug allergy may require graded oral challenge under supervision. Differential diagnoses to exclude include vasovagal syncope, panic attack, acute asthma without systemic involvement, scombroid poisoning (histamine in spoiled fish), carcinoid syndrome, pheochromocytoma, hereditary angioedema (no urticaria, no bronchospasm, slower onset), and septic shock.
With prompt epinephrine and proper follow-up, the prognosis is excellent — overall case-fatality from anaphylaxis is 0.7-2 per million person-years in population studies. The dominant predictors of death are delayed epinephrine, untreated asthma, adolescence with food allergy, and severe upfront cardiovascular collapse. Patients who experience a single uncomplicated episode and receive specialist follow-up, an action plan, and two auto-injectors have a less than 1% risk of fatal future reaction if these resources are used correctly. Recurrence over 5 years approaches 25-30% in food allergy and over 50% in venom allergy without immunotherapy, but specific allergen immunotherapy reduces recurrence to under 5%. Children with milk, egg, wheat, and soy allergy often outgrow them by adolescence (50-80%); peanut, tree nut, fish, and shellfish allergies typically persist for life. Death from anaphylaxis remains rare relative to incidence, but every death is largely preventable, and the chain of survival depends on rapid recognition, immediate IM epinephrine, and access to emergency care within minutes.
Every patient with one episode of anaphylaxis should be referred to an allergy & immunology specialist for trigger confirmation, action-plan tailoring, and consideration of immunotherapy. Allergists perform skin and component-resolved testing that primary care cannot, supervise food and drug challenges, and identify cofactor-augmented or mast-cell-driven cases. Recurrent idiopathic anaphylaxis or baseline tryptase above 11.4 ng/mL warrants combined allergy-hematology workup for mast-cell disorders.
Find specialists →Uncomplicated anaphylaxis treated promptly resolves clinically within 30-60 minutes of epinephrine administration. Patients are observed for at least 4 hours — longer (8-24 hours) if there was hypotension, severe respiratory involvement, multiple epinephrine doses, or limited access to emergency care for the next 24 hours. Biphasic recurrence appears in approximately 5-20% of cases, typically 1-12 hours (median 8-10 hours) after initial recovery (Lieberman 2005; Alqurashi 2017). Most patients return to normal activity within 24-48 hours. Cognitive and emotional sequelae (anxiety, hypervigilance, post-traumatic stress) are under-recognized and benefit from formal allergy follow-up and, where needed, psychological support.
Regular exercise is safe and encouraged for people with anaphylaxis history, except where food- or drug-dependent exercise-induced anaphylaxis has been diagnosed. In those cases, avoid trigger foods for at least 4 hours before exercise and never exercise alone in the first weeks after diagnosis. Always carry an epinephrine auto-injector during physical activity, and ensure exercise partners and coaches know how to use it.
Look for board certification in allergy & immunology (or pediatric allergy for children), experience with venom and food immunotherapy, in-house oral food and drug challenge capability, and access to component-resolved IgE testing. Confirm the practice provides a written, signed anaphylaxis action plan and trains patients and family members on auto-injector technique. For perioperative anaphylaxis, an allergist with specific drug-allergy expertise and links to anesthesia is essential.
Medically reviewed by AIHealz Medical Editorial Board · May 12, 2026
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