Purpose:
A prick test is often used by allergists when a patient has clear allergy symptoms but is not certain which food is causing those symptoms (or whether the symptoms are caused by a food at all). They are often used when patients have hives, eczema, or hay fever symptoms.Time:
20 to 30 minutes.Advantages:
Prick tests are among the quickest allergy tests available. They are reasonably inexpensive, allow allergists to test a number of potential allergens at one time, and are usually not painful.Disadvantages:
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.
How it works:
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.)
