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Anaphylaxis is a medical emergency that requires immediate diagnosis and treatment. Definitions of anaphylaxis have conflicted over the years, but recent clarity has emerged based on consensus symposia. In simple terms, “anaphylaxis is a serious allergic reaction that is rapid in onset and may cause death.”1,2 More detailed revisions of the definition2 for health professionals using clinical criteria suggest anaphylaxis is highly likely when any one of the three criteria listed in Table 27-1 occurs.1

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Table 27-1 Clinical Criteria for Anaphylaxis 
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The traditional nomenclature for anaphylaxis reserves the term anaphylactic for immunoglobulin E (IgE)-dependent reactions and the term anaphylactoid for IgE-independent events, which do not require a sensitizing exposure. As the final pathway in classic anaphylactic and anaphylactoid reactions is identical, anaphylaxis is the term now used to refer to both IgE and non-IgE reactions (e.g., IgE-independent, IgG- and immune complex complement–mediated).3

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Hypersensitivity is an inappropriate immune response to generally harmless antigens. Anaphylaxis represents the most dramatic and severe form of immediate hypersensitivity. Anaphylaxis occurs as part of a clinical continuum. It can begin with relatively minor symptoms and rapidly progress to a life-threatening respiratory and cardiovascular reaction.

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Epidemiology

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Foods, medications, insect stings, and allergen immunotherapy injections are the most common provoking factors for anaphylaxis, but any agent capable of producing a sudden degranulation of mast cells or basophils can induce anaphylaxis. A significant number of anaphylaxis cases reported have no identified cause (idiopathic anaphylaxis).

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β-Lactam antibiotics are estimated to cause 400 to 800 deaths in the U.S. annually, with a systemic allergic reaction occurring in 1 per 10,000 exposures.3 Hymenoptera stings constitute the next most common cause of anaphylaxis, with fewer than 100 deaths in the U.S. annually.3Table 27-2 contains a partial list of the more common causative agents, but the causes vary geographically and with age....

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