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The history of your symptoms is important in diagnosing all
allergies, including whether the symptoms vary according to time of
day, season, exposure to pets and other potential allergens, and
diet changes. Severe reactions often develop very quickly after
exposure, such as eating culprit nuts or getting stung. Allergy
testing may be required to determine if your symptoms are an actual
allergy or caused by other problems. For example, eating
contaminated food (food poisoning) may cause symptoms that resemble
food allergies. Some medications (such as aspirin, ampicillin, and
others) can produce non-allergic reactions, including rashes, that
resemble drug allergies but are not true allergies.
Tests that may reveal the specific allergens include:
- Skin testing -- the most common method of
allergy testing. This may include intradermal, scratch, patch,
or other tests. Skin testing may even be an option for young
children and infants, depending on the circumstances.
- Blood test -- also called RAST (radioallergosorbent),
this measures the levels of allergy antibody, IgE, produced when
your blood is mixed with a series of allergens in a laboratory.
If you are allergic to a substance, the IgE levels may increase
in the blood sample. The blood test may be used if you have
existing skin problems like eczema, if you're on medications
that are long-acting or you cannot stop taking, if you have a
history of anaphylaxis, or if you prefer not to have a skin test.
- "Use" or "elimination" tests -- suspected
items are eliminated and/or introduced while the person is
observed for response to the substance. This is often used to
check for food or medication allergies.
- Eyelid -- Occasionally, the suspected
allergen is dissolved and dropped onto the lining of the lower
eyelid (conjunctiva) as a means of testing for allergies. (This
test should only be done by a physician, never the patient,
since it can be harmful if done improperly.)
- Reaction to physical stimuli -- application
of heat, cold, or other stimulation, and then look for an
allergic response.
Other tests that may reveal allergies include:
- Antibody/immunoglobulin (particularly IgE) levels -- when
these are elevated, it indicates a "primed" immune system.
- CBC -- may reveal an increase in eosinophils.
- Complement levels -- may be abnormal
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