Anaphylaxis Diagnosis

The diagnostic criteria for anaphylaxis was written in 2005/2006 by a panel of experts.   The criteria has a sensitivity of 97% and specificity of 82%.   Skin symptoms are present in 90% of anaphylactic cases.  Diagnosis is highly probable if one of the three following criteria are met.

Table 1 – Anaphylaxis Diagnostic Criteria

Criteria

Criteria Cont.

1: Acute onset of symptoms involving the skin (hives, pruritus, flushing)  and/or mucosal tissue (swelling of uvula, tongue, lips) and one of the following:

  • Respiratory distress (wheezing, stridor, hypoxia)
  • Hypotension or symptoms of hypotension (syncope, collapse)

2: Rapid development of two or more of the following symptoms following exposure to an allergen

  • Skin/mucosal symptoms
  • Respiratory distress
  • Hypotension
  • GI distress (cramping, nausea, vomiting, diarrhea)

3: Hypotension after exposure to a known allergen defined as

Definition of Hypotension

  • Systolic < 90 or a greater than 30% decrease from baseline BP
  • Pediatrics - Greater than a 30% decrease from baseline or Systolic BP <70 for infants 1 month to 1, < 70 mmHg + [2 x age]) from 1-10y >10y see adult criteria

Clinical judgment is imperative in patients who do not meet the criteria but still require treatment.  A patient who has only skin symptoms or mucosal symptoms but has a history of near-fatal anaphylaxis from a particular allergen warrants treatment if exposed to that allergen.

Lab testing is not routinely done in emergency situations to confirm the diagnosis.  Treatment should not be withheld while awaiting laboratory confirmation.  An elevated blood histamine or tryptase can confirm the diagnosis in situations where the initial diagnosis was not clear.

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