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Something in the Air: Airborne
Allergens
Diagnosing Allergic Diseases
People with allergy symptoms, such as the runny nose of allergic
rhinitis, may at first suspect they have a cold--but the "cold"
lingers on. It is important to see a doctor about any respiratory
illness that lasts longer than a week or two. When it appears
that the symptoms are caused by an allergy, the patient should
see a physician who understands the diagnosis and treatment
of allergies. If the patient's medical history indicates that
the symptoms recur at the same time each year, the physician
will work under the theory that a seasonal allergen (like pollen)
is involved. Properly trained specialists recognize the patterns
of potential allergens common during local seasons and the association
between these patterns and symptoms. The medical history suggests
which allergens are the likely culprits. The doctor also will
examine the mucous membranes, which often appear swollen and
pale or bluish in persons with allergic conditions.
Skin Tests
Doctors use skin tests to determine whether a patient has IgE
antibodies in the skin that react to a specific allergen. The
doctor will use diluted extracts from allergens such as dust
mites, pollens, or molds commonly found in the local area. The
extract of each kind of allergen is injected under the patient's
skin or is applied to a tiny scratch or puncture made on the
patient's arm or back.
Skin tests are one way of measuring the level of IgE antibody
in a patient. With a positive reaction, a small, raised, reddened
area (called a wheal) with a surrounding flush (called a flare)
will appear at the test site. The size of the wheal can give
the physician an important diagnostic clue, but a positive reaction
does not prove that a particular pollen is the cause of a patient's
symptoms. Although such a reaction indicates that IgE antibody
to a specific allergen is present in the skin, respiratory symptoms
do not necessarily result.
Blood Tests
Although skin testing is the most sensitive and least costly
way to identify allergies in patients, some patients such as
those with widespread skin conditions like eczema should not
be tested using that method. There are other diagnostic tests
that use a blood sample from the patient to detect levels of
IgE antibody to a particular allergen. One such blood test is
called the RAST (radioallergosorbent test), which can be performed
when eczema is present or if a patient has taken medications
that interfere with skin testing.
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