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

• 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