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A bronchoprovocation test usually consists of inhaling a chemical such as histamine or methacholine that causes bronchoconstriction in most asthmatics and a much smaller percentage of people without asthma at low concentrations. At higher concentrations more normal people bronchoconstrict. A response with a low dose suggests asthma, although again some people without asthma can respond and no response strongly suggests the person does not have asthma. The way the bronchoconstriction is measured is by doing spirometry after every dose. A specific bronchochallenge test would be for the person to inhale whatever the suspected allergen causing bronchoconstriction is. This is seldom used but in very special circumstances can be used.