watery eyes, itching, rash, and sometimes even life-threatening anaphylactic shock.
Allergy testing is performed to find out what exactly an individual is allergic to. Skin
tests are most often done to identify the cause of sneezing, runny nose, and nasal
congestion of hay fever or the wheezing of asthma. Patch tests are done to help
diagnose unexplained rashes. Allergy tests are usually done by a doctor or technician.
The three types of allergy tests are the scratch test, the intradermal test, and the Patch
(a) The scratch test. This test is used often because the reaction it can
produce is less severe in a person who is highly allergic to substances. In this test, very
small amounts of dilute solutions of different suspected allergens (grasses, weeds,
trees, molds, dusts, and foods) are placed on the patient's arm or back. The skin
beneath the sample is lightly scratched with a sterile pin. After twenty to thirty minutes,
the scratched areas are examined for a reaction such as redness, swelling, and
blistering. The entire test usually takes about thirty to forty minutes and may be
(b) The intradermal test. In this test, small amounts of various
suspected allergens are injected into the skin on the patient's arms or back. After
twenty to thirty minutes, the injection sites are evaluated for reactions.
(c) The Patch test. Diluted samples of suspected allergens are placed
on small pieces of filter paper and taped to the skin on the patient's back. The patches
are left in place for twenty-four to forty-eight hours. During this period, the patient
should not bathe or engage in any activity that might cause him to sweat and loosen the
patches. After the required number of hours, the patches are removed, and any skin
reactions under the patches are examined.
(2) Tuberculosis tests. The purpose of a tuberculin skin test is to determine
whether the person was ever infected by the bacterium that causes tuberculosis. The
individual's immune system will produce swelling at the injection site one to two days
after the skin test if that person has been infected with tuberculosis or vaccinated
against tuberculosis any time in the past. Two commonly used skin tests are the tine
test and the Mantoux test. The tine test uses dried, old tuberculin (OT) on several metal
tines embedded in a round plastic head. The tines are pressed against the person's
skin, and the antigen enters the dermis layer of skin. This method is convenient and
safe for mass surveys. The most accurate method of tuberculin testing is the Mantoux
test, which requires injection of antigen into the epidermal skin layer.