Criteria for diagnosis in emergency settings are listed in the article. The criteria necessary for the diagnosis are fewer if the offending allergen is suspected or known.
Non IgE mediated (e.g. from radiocontrast media) reactions are considered anaphylaxis although an alternate terminology labels them as anaphylactoid.
Among the cutaneous manifestations hives are the most characteristic but flushing, pruritis and angioedema are also listed.
A biphasic response occurs in up to 20% of patients. Observation for 8-12 hours is recommended.
Though antihistamines are the most common first line drugs used that is not a recommended practice. Epinephrine is first line treatment. As explained in the article:
Diphenhydramine is the most common drug given in the ED, even though it takes up to 80 minutes for 50% suppression of histamine flare and only affects the histamine mediator of anaphylaxis.28 Corticosteroids are the second most commonly administered drug in an emergency situation, but they also work slowly. Epinephrine is the treatment of choice as a first response because it acts on multiple receptors and has a maximal pharmacodynamic effect within 10 minutes of intramuscular (IM) administration into the thigh.29, 30 Multiple groups, including the NIAID, the WAO, the International Collaboration in Asthma and Allergy, and the Joint Task Force on Practice Parameters (representing several professional allergy/asthma organizations) state that epinephrine is an essential treatment for anaphylaxis.
Not all anaphylaxis is categorized as anaphylactic shock. The author says epinephrine should be given any time the diagnosis of anaphylaxis is made even in the absence of shock or severe respiratory manifestations.
Concerning the underlying triggers, the article states:
Foods (35%) represent the most common triggers for allergic reactions, followed by drugs and biologics (20%), insect stings (20%), exercise (5%), and vaccines (3%).22 Idiopathic or unknown causes account for approximately one fifth of remaining cases. Although triggers ultimately may be found for most cases of idiopathic anaphylaxis, there does seem to be an intrinsic disorder, currently unidentified, linked to some allergic reactions.