Anaphylaxis (cont.)

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How common is anaphylaxis?

Current estimates put the number of annual deaths in the U.S. due to anaphylaxis at approximately 1,500 per year. Although anaphylaxis can be due to different causes, there are four major subtypes of anaphylaxis (reactions to food, drugs, latex, and insect stings). Depending on the substance causing anaphylaxis, the rate of anaphylaxis upon exposure to a substance has been estimated to be between less than 1% to up to 10%.

What are common causes of anaphylaxis?

The causes of anaphylaxis are divided into two major groups:

  • IgE mediated: This form is the true anaphylaxis that requires an initial sensitizing exposure (for example, an exposure to the substance that will later trigger the anaphylaxis) and occurs on a subsequent exposure. It involves the coating of mast cells and basophils (cells in the blood and tissue that secrete the substances that cause allergic reactions, known as mediators) by IgE, and the explosive release of chemical mediators upon reexposure.
  • Non-IgE mediated: These reactions, the so called "anaphylactoid" reactions, are similar to those of true anaphylaxis but do not require an IgE immune reaction. They are usually caused by the direct stimulation of the mast cells and basophils. The same mediators as occur with true anaphylaxis are released and the same effects are produced. This reaction can happen, and often does, on initial as well as subsequent exposures, since no sensitization is required.

The terms anaphylaxis and anaphylactoid (meaning "like anaphylaxis") are both used to describe this severe allergic reaction. Anaphylaxis is used to describe reactions that are initiated by IgE and anaphylactoid is used in reference to reactions that are not caused by IgE. The effects of the reactions are the same, however, and are generally treated in the same manner. Often, they can not be distinguished initially.

Although it may appear that IgE mediated anaphylaxis occurs upon a first exposure to a food, drug, or insect sting, there must have been a prior, and probably unwitting, sensitization from a previous exposure. You may not remember an uneventful sting or be aware of "hidden" allergens in foods.

Medically Reviewed by a Doctor on 10/22/2013

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