Hay Fever (cont.)
How is allergic rhinitis diagnosed, and how are allergies identified?
If a person is experiencing the typical symptoms of hay fever, a consultation with an allergy specialist can help identify the offending substances. Since the ideal way to manage an allergy is to avoid the substances that cause allergic reaction, it is therefore very important to first identify these substances (allergens). Many allergens can be suspected from information obtained in a patient's particular history. For example, if symptoms usually worsen with exposure to cats, then cat protein is a probable allergen causing the symptoms. If cutting grass is associated with the onset of symptoms, then grass allergy is probable. A patient's history of reactions is very important in determining his/her unique allergies.
Because the identification of allergens is important and often difficult
to pinpoint, skin testing is often needed to identify exactly the specific
substance causing the allergy. Skin testing is now done with minimal
discomfort and is performed as follows:
- A small amount of the suspected allergy substance is placed on the skin.
- The skin is then gently scratched through the small drop with a special sterile needle. This is known as the prick-puncture method and is typically used for initial evaluations. A second method, known as the intradermal method, involves injection of a small amount of the test substance into the skin. Intradermal testing is more sensitive but also tends to lead to more false-positive results.
- If the skin reddens and, more importantly, swells, then an individual is said to be "sensitized" to the particular allergen. If typical symptoms occur when a sensitized individual is exposed to the suspected substance, then allergy to that substance is probable.
- The skin testing described is tolerated by the youngest of patients and should be the standard of testing.
- Skin testing is not indicated for people who are at risk of a severe (anaphylactic) allergic reaction, who have certain skin conditions, or who are taking certain medications.
A number of blood tests are also available to aid in the diagnosis of allergy. These blood tests may be useful in people who cannot be skin tested due to skin diseases, who are taking medications that interfere with skin testing, or who are at a high risk of having an anaphylactic reaction to skin testing. These blood tests typically use various techniques to look for IgE antibodies in the blood and by inference suggest allergy in the tissues. If the allergy testing agrees with the history of symptoms upon exposure to the substance, then a diagnosis of allergic rhinitis is likely.
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