If symptoms don't improve with self-help steps and over-the-counter drugs, and your history suggests an allergy, your doctor might recommend a referral to an expert in allergy or immunology for testing.
There are many different ways in which an allergy can be diagnosed and can depend on the type of allergy and age of the patient.
Different allergens bother different people, so your allergist will determine which test is the best for you. Regardless of the type of test, an allergist will first perform a physical examination and ask questions about your symptoms to determine if allergy testing is warranted.
Skin Prick Tests (SPT):
This type of testing is the most common and is relatively painless.
SPT is usually carried out on the inner forearm, but in some circumstances may be carried out on another part of the body, such as back or thigh. For example, there is a larger area on the back or thigh to perform testing on a baby, similarly, for those with troublesome eczema the test can be performed on any clear patch of skin.
The test allergens are selected following a discussion with your clinician and based on your history. The skin is coded with a marker pen to identify the allergens to be tested. A drop of the allergen (extract) solution is placed on the skin. The skin is then pricked through the drop using the tip of a lancet – this can feel a little sharp but should not be painful and should not bleed.
If you have allergies, just a little swelling that looks and feels like a mosquito bite will occur where the allergen(s) to which you are allergic was introduced. If you are allergic to house dust mite, but not to pollen, only the house dust mite allergen will cause a little swelling or itching. The spot where the pollen allergen was applied will remain normal.
You don't have to wait long to find out what is triggering your allergies. Reactions occur within about 20 minutes. And you generally won't have any other symptoms besides the small hives where the tests were done, which go away within 30 minutes. If your prick skin tests are negative but your physician still suspects you might have allergies, more sensitive “intradermal” tests may be used in which a small amount of allergen is injected within the skin.
Skin tests are best performed in an allergist's office to assure the test results are read properly and to minimize the risk of rare side effects.
A very small amount of an allergen is inhaled or taken by mouth. Challenges are done mostly with potential food or medication allergies. It is very important that they be supervised by a physician with specialized training and experience, such as an allergist.
This test involves drawing blood, so results are not available as rapidly as with skin tests. Blood tests are generally used when skin tests might be unsafe or won't work, such as if you are taking certain medications, or have a skin condition that may interfere with skin testing.