Prick tests are considered less sensitive than some other allergy tests, and a negative prick test may be followed up with other, more sensitive tests if a practitioner strongly suspects an allergy. Prick tests are generally not used when a reaction is considered life-threatening.
"False positives," where a food someone tolerates well returns a positive test result, do sometimes occur. An allergist will make a final diagnosis of an allergy based not just on the prick test, but also on the patient's symptoms and history.
Prick tests (sometimes called scratch tests) are performed on the skin of the forearm or the back. Allergists put a small amount of an extract of a potential allergen into a shallow scratch. Within twenty to thirty minutes, a positive result will show as a hive, or wheal, on the scratch. The size of the hive may correlate with the intensity of the allergic reaction.
In the event of a severe reaction, the allergist will administer a rescue medication such as epinephrine or an antihistamine. Severe reactions to a prick test, however, are uncommon. (This is why they are generally not used to confirm life-threatening reactions -- blood tests are much safer for that purpose.)
