Anaphylaxis is a serious generalized or systemic hypersensitivity reaction that is rapid in onset and potentially fatal.

Diagnosis can be made if it is acute in onset of minute to several hour duration that involves the skin, mucosal tissue or both plus having signs & symptoms either respiratory or cardiovascular compromise.

It involves immunological response with IgE, IgG or immune complexes. Non-immunological mechanisms are also involved and termed as nonallergic anaphylaxis that is relatively uncommon in children.

Protracted, severe anaphylaxis are reactions occurring up to 32 hours despite aggressive management.



Diagnosis of anaphylaxis is highly likely when any one of the following 3 criteria is fulfilled

  • Acute onset of illness of minutes to several hours duration involving the skin, mucosal tissue, or both (eg pruritus, flushing, generalized hives, edema of lips, tongue and uvula)
  • Plus at least one of the following:
    • Respiratory compromise (eg dyspnea, stridor, wheezing, hypoxia)
    • Cardiovascular compromise or end-organ dysfunction symptoms (eg hypotension, collapse, syncope, incontinence)
  • ≥2 of the following that occur rapidly after exposure to a likely allergen of minutes to several hours duration
    • Skin or mucosal tissue involvement (eg pruritus, flushing, generalized hives, edema of lips, tongue and uvula)
    • Respiratory compromise (eg dyspnea, stridor, wheezing, hypoxia)
    • Cardiovascular compromise (eg hypotension, collapse)
    • GI symptoms that are persistent (eg crampy abdominal pain, vomiting)
  • Decreased BP after exposure to known allergen of minutes to several hours duration
    • Hypotension is defined as:
      • SBP <60 mmHg for term neonates (0-28 days)
      • SBP <70 mmHg for 1 month-1 years of age
      • SBP < [70 mmHg + (2 x age)] for 1-10 years of age
      • SBP <90 mmHg for 11-17 years of age


  • A key part of the diagnostic work-up
  • Important to identify risk & predisposing factors for possible recurrence (eg history of previous anaphylactic reactions, history of atopy, asthma even if well-controlled, adolescence, family history of any type of allergic reaction)
    • Family history remains the most practical and useful tool in identifying allergy-prone infants
    • Presence of allergic diseases in one or both parents and in a sibling increases likelihood of allergy in a child
  • Determine and record the time of onset of symptoms and the circumstances prior to the reaction
    • Obtain a detailed history of all the food and drugs taken, and all the patient’s activities, including history of sting or bite, over the 4-6 hours period prior to the episode

Laboratory Tests

  • Given a reliable history, serum specific IgE, skin prick test and food patch test will confirm the diagnosis
    • However, anaphylaxis may be seen in patients without cutaneous manifestations or specific IgE
    • Skin prick and in vitro tests may help identify specific IgE antibodies reacting to the etiologic agent
  • Food challenge is warranted in patients with a history of life-threatening anaphylaxis when the causative agent cannot be conclusively determined by history and laboratory exam, or if the patient is believed to have outgrown their food sensitivity
    • May include exercise testing if exercise is considered an amplifying factor
  • Testing serum tryptase level is not specific for anaphylaxis but can sometimes be useful to support the clinical diagnosis of anaphylaxis
    • Acquire a sample right after starting emergency treatment
      • Acquire a second sample within 1-2 hours (but no later than 4 hours) from onset of symptoms
      • May be elevated for up to 12 hours in drug-induced and bee-sting anaphylaxis; however, serum elevation is also noted in systemic mastocytosis
    • Rarely elevated in food anaphylaxis in children
    • Degree of elevation is associated with the degree of hypotension
    • Normal levels do not exclude diagnosis of anaphylaxis
  • Other tests to be considered include urinary 5-hydroxyindoleacetic acid, urinary methylhistamine, chromogranin A, vasointestinal polypeptide, oligosaccharide alpha-gal antibodies (for red meat hypersensitivity in persons with history of tick bites), and catecholamines
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