Anaphylaxis is an acute-onset, potentially fatal systemic
allergic reaction. It is usually triggered by an agent such as an
insect sting, food, or medication, through a mechanism involving
IgE and the high-affinity
IgE receptor on mast cells or basophils. Less commonly, it is triggered through other immunologic mechanisms, or through nonimmunologic mechanisms. It often occurs in community settings.
Anaphylaxis episodes range in severity from those that are mild and resolve spontaneously to those that are fatal within minutes. The clinical diagnosis is based on a meticulous history and physical examination, sometimes, but not necessarily, supported by a laboratory test such as an elevated serum total
tryptase level. Sensitization to
allergen triggers suggested by the history needs to be confirmed by skin testing and measurement of
allergen-specific
IgE. In some sensitized individuals, additional tests are needed to assess the risk of future
anaphylaxis episodes. Prompt injection of
epinephrine is life-saving. H1-antihistamines and inhaled beta2-adrenergic agonists cannot be depended on to prevent fatality. Long-term risk reduction is an integral part of management.