There are a number of studies offering guidelines for the diagnosis of anaphylaxis. The consensus of the expert panel convened by ACAAI and ACEP was that the clinical criteria for diagnosing anaphylaxis as set forth in the Second National Institute of Allergy and Infectious Disease (NIAID)/Food Allergy and Anaphylaxis Network (FAAN) symposium provides an easy-to-use guide, and is an appropriate reference for use by physicians who suspect anaphylaxis in the emergency setting:

Clinical Criteria for Diagnosing Anaphylaxis1 Anaphylaxis is highly likely when any one of the following 3 criteria is fulfilled: 1. Acute onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both (e.g. generalized hives, pruritus or flushing, swollen lips-tongue-uvula) AND AT LEAST ONE OF THE FOLLOWING:   Respiratory compromise (e.g., dyspnea, wheeze-bronchospasm, stridor, reduced PEF, hypoxemia)   Reduced BP or associated symptoms of end-organ dysfunction (e.g., hypotonia [collapse], syncope, incontinence) 2. Two or more of the following that occur rapidly after exposure to a likely allergen for that patient (minutes to several hours):   Involvement of the skin/mucosal tissue (e.g., generalized hives, itch-flush, swollen lips-tongue-uvula)   Respiratory compromise (e.g., dyspnea, wheeze-bronchospasm, stridor, reduced PEF, hypoxemia)   Reduced BP or associated symptoms (e.g., hypotonia [collapse], syncope, incontinence)   Persistent gastrointestinal symptoms (e.g., crampy abdominal pain, vomiting) 3. Reduced BP after exposure to known allergen for that patient (minutes to several hours)   Infants and children: low systolic BP (age specific) or greater than 30% decrease in systolic BP*   Adults: systolic BP of less than 90 mm Hg or greater than 30% decrease from that person’s baseline PEF, Peak expiratory flow; BP, blood pressure. *Low systolic blood pressure for children is defined as less than 70 mm Hg from 1 month to 1 year, less than (70 mm Hg + [2 x age]) from 1 to 10 years, and less than 90 mm Hg from 11 to 17 years. Posted with permission from Journal of Allergy and Clinical Immunology

1. Sampson HA, Munoz-Furlong A, Campbell RL, Adkinson NF, Bock SA, Branum A, Brown S, Camargo CA, Cydulka R, Galli SJ, Gidudu J, Gruchalla RS, Harlor, AD, Hepner DL, Lewis LM, Lieberman PL, Metcalfe DD, O’Connor R, Muraro A, Rudman A, Schmitt C, Scherrer D, Simons FER, Thomas S, Wood JP, Decker WW. Second symposium on the definition and management of anaphylaxis: Summary report-Second National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network symposium. J Allergy Clin Immunol 2006;117(2):391-397.