Question of the Week: February 27, 2012

Question: What is the difference between an anaphylactic and an anaphylactoid reaction?

Answer: An anaphylactic reaction involves prior sensitization and the immunoglobulin IgE. When the body is re-exposed to an antigen, it combines with IgE antibodies on mast cells and basophils. Once this binding occurs, chemical mediators such as histamine, leukotrienes and prostaglandins are released, causing the anaphylactic reaction. An anaphylactoid reaction causes the release of these mediators without IgE or prior sensitization. This is why someone may have a significant reaction without prior exposure. Some substances known to cause these anaphylactoid reactions are opioids, NSAIDS and radiopaque contrast (X-Ray) media.

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