There are few ways to test someone to find out if they are allergic or not. Depending on the symptoms of the patient, patient story and what we found in examination, we choose the correct allergy testing method. No matter what test is used, one needs to connect the dots to see if results are meaningful for the patient's allergy problem. For example, if a patient has year long symptoms and is found to be allergic to only grass pollen, one should not blame grass pollen for the patient's yearlong misery and look for answers elsewhere.
Allergy testing methods:
Prick and intradermal skin test
The prick or intradermal skin test involves injecting a small amount of allergen into the skin and then health care provider monitoring patient for a reaction at the site. This test is designed to determine if you have allergies to what you inhale, medications, food, venom and latex.
How is the prick or intradermal test done?
- Skin testing is typically done on the back, forearm or arm.
- Skin is pricked with skin testing device containing a tiny amount of allergen which introduces minisule amount of allergen in the superficial layer of the skin. Process is very similar for intradermal skin test except a slightly higher amount of allergen is introduced in the deeper layer of the skin called dermis, hence the name intradermal skin test.
- Patients who are allergic to any of the allergens would see swelling (called wheal) and redness (called flare) at the site of the test within 15-20 minutes which usually goes away in 30 minutes.
- Results are read by a board certified allergist.
- Interpretations of test results are discussed with the patient.
Blood allergy test
- Can help in certain patients when patients are unable to discontinue allergy medications, and cannot be tested due to skin diseases, or patient preference.
- Has value in selected patients with food allergies to help decide if they can tolerate the food.
- It has value in selected patients with bee, wasp, yellow jacket and hornet allergy.
- there are some allergens for which there is no skin test available.
- In general, the blood allergy test are less sensitive (may miss allergies in many instances), are more expensive, and take more time to have results.
Skin patch testing
Designed to assess allergy to what comes in contact with skin such as metals, perfumes, and skin care products. Patch testing is different than prick skin test as this is used to detect different kind of allergies. Patch tests identifies allergen specific T-lymphocytes as opposed to allergen specific antibodies. The way patch test is done is different and more time consuming.
Does everyone need allergy testing who sees an allergist?
Many patients need allergy testing, but not every patient needs allergy testing at all or it may be done at a time jointly decided by the patient and an allergy doctor.
How should you prepare before you come in for skin testing?
Allergy medications like antihistamines interfere with interpretation of the test and may result in false negative test. Some medications are okay to take before allergy test and others are not. Please visit Antihistamines resource page for medications which may be taken before the test and which need to be discontinued.