See alsoALLERGIC CONJUNCTIVITIS; ALLERGY TESTING;
ANGIOEDEMA; ASTHMA; FOOD ALLERGIES; LIVING WITH
ALLERGIES.
allergy testing Diagnostic procedures to deter-
mine the allergens responsible for HYPERSENSITIVITY
REACTION. The most specific ALLERGY test is the
allergy SKINtest, also called a scratch test or a
patch test. For this test, the allergist uses the inside
of the arm or a section of the back to expose the
body to suspected allergens. The allergist places a
small drop of a solution containing the ALLERGEN
on a marked spot on the skin, then uses a sterile
picklike instrument to scratch the surface of the
skin. This exposes the IMMUNE SYSTEMto the sus-
pected allergen. If a WHEAL(raised welt) forms on
the site within 15 minutes, the test is positive for
the allergen. For a typical allergy skin test, the
allergist may test a number of substances at the
same time, each on a different site on the skin.
The allergy skin test tells the allergist the precise
allergies an individual has. The allergy skin test
helps the allergist strategize the most effective
treatments and is necessary before DESENSITIZATION
treatments.
Though it is rare, a person who has a
strong allergy may have an intense reac-
tion during an allergy SKINtest, includ-
ing ANAPHYLAXIS, that requires urgent
medical treatment.A radioallergosorbent test (RAST) is a blood test
that measures the amount of IMMUNOGLOBULIN E
(IgE) in the BLOODcirculation when allergy symp-
toms are present. An amount higher than normal
level of serum IgE indicates a hypersensitivity
reaction. The RAST does not identify the specific
allergen. There is no risk for the RAST to cause a
hypersensitivity reaction because it does not
expose the person to any allergens.
A food-elimination diet is the preferred allergy
test to identify potential FOOD ALLERGIES. The per-
son eliminates specific foods from his or her diet
for several weeks, then reintroduces them one at a
time and notes whether there are corresponding
symptoms. An important part of a food-elimina-
tion diet is keeping an accurate food diary that
records symptoms and other perceptions during
the test. This allergy test is somewhat subjective,
though often results in connecting specific foods
with allergy symptoms. Another test for food
allergies is the food challenge, which takes place
in a hospital. The allergist gives the person certain
foods, often mixed with other foods, without the
person knowing, then observes and documents
any symptoms that develop. There is a risk that
the food challenge may cause a hypersensitivity
reaction that would require immediate medical
intervention; this is why the test takes place in a
hospital or other emergency-ready facility.
See also ALLERGEN; ALLERGIC CONJUNCTIVITIS;
ALLERGIC DERMATITIS; ALLERGIC RHINITIS; ANAPHYLAXIS.anaphylaxis A severe HYPERSENSITIVITY REACTION
(allergic reaction) in which the tissues of the
throat swell, preventing air from getting to the
LUNGS. Anaphylaxis, also called anaphylactic
shock, is a type I hypersensitivity reaction that
often develops rapidly, within minutes to an hour
of exposure to the ALLERGEN. Hives, ANGIOEDEMA,
and airway spasms are the most common symp-
toms. Some people also experience numbness or
tingling of the lips and MOUTH. Though anaphy-
laxis can be life-threatening, with prompt and
appropriate treatment it is seldom fatal.
The first line of treatment is EPINEPHRINEand
antihistamine administered by injection, which
immediately and effectively stop the progression
of the hypersensitivity reaction. When airway
(bronchial) symptoms are severe, the doctor may
also administer an injectable corticosteroid med-
ication. Swelling and related symptoms usually
abate within a few minutes. Supportive treatment
for symptoms often includes OXYGEN THERAPYand
intravenous fluids. Most people completely
recover within a few hours.
Bee stings, peanuts, intravenous penicillin, and
intravenous contrast dyes for radiology procedures
are the most common allergens responsible for
anaphylaxis. However, anaphylaxis is possible
with any ALLERGY. Anaphylaxis is fatal for about
200 Americans each year. Some people may bene-
fit from DESENSITIZATION, depending on the allergen
responsible for the hypersensitivity reaction, to
mitigate theIMMUNE RESPONSEwith future expo-
sures. People who know they have severe allergies
may get a doctor’s prescription for an anaphylaxis244 The Immune System and Allergies