Anaphylaxis

What it is

Anaphylaxis is an acute (within minutes, or up to a few hours), potentially life-threatening systemic allergic reaction which can be caused by numerous triggers. It is a hypersensitivity reaction involving the release of mediators from mast cells, basophils and recruited inflammatory cells. It can be mild, moderate to severe, or severe; most cases are mild, but any anaphylaxis has the potential to become life-threatening, often within minutes. Anaphylactic shock is not the same word: it is the circulatory shock caused by low blood pressure from the widespread vasodilation of degranulation, and by definition it is a blood pressure 30% below the patient's baseline or below standard values, 90 systolic for adults. Anaphylaxis is type 1 hypersensitivity and is mostly histamine mediated, whereas an anaphylactoid reaction is bradykinin mediated, for example a CT contrast mediated allergic reaction. The anaphylactic reaction requires prior sensitization or cross-reactivity, cannot occur on first exposure, and is predicted by allergy skin tests; the anaphylactoid reaction requires no prior sensitization, can occur on first exposure, usually needs more exposure than anaphylaxis, and is not predicted by skin tests.