Allergy skin testing helps diagnose allergies. Allergy skin testing can identify 10 to 50 specific substances, called allergens, which cause allergy symptoms in children and adults. An allergist will interpret your allergy skin testing results in relation to your medical history, physical exam, and other tests. An allergist, also known as an allergist-immunologist, has the specialized skills and experience needed to read allergy skin testing results properly. Allergy skin testing is only one method used to diagnose allergies.
Information from allergy tests may help your doctor develop an allergy treatment plan that includes allergen avoidance, medications or allergy shots (immunotherapy).
Allergy skin tests are widely used to help diagnose allergic conditions, including:
Hay fever (allergic rhinitis)
Bee venom allergy
-Low cost, high sensitivity and rapid results
-Allows prediction of disease and follow up of any disease development
-May be affected by medication and skin condition.
-Potential to cause adverse reaction.
-Responsiveness depends on age.
-Inconvenient for patient.
-Requires skill and expertise.
First, the nurse will mark areas on the skin of your arm or back and label them for the types of allergens that will be used in the skin test. A drop of an allergen extract will then be applied next to each mark and a small lancet will be used to gently prick the extracts into the skin. In approximately 20 minutes, the results can be read. The types of allergens chosen for use in the skin test are dependent on the medical history of each individual patient.
You will be asked to not take any antihistamines for 3 to 7 days before the test. You will discuss with your doctor when to stop taking them. It’s okay to use nose [nasal] steroid sprays and asthma medicines. They will not interfere with skin tests. Talk to your doctor before the testing to find out which medications you can continue using.
If the patient is allergic to a certain substance, a raised reddish spot (hives) will develop along with, possibly, some mild itchiness at the test location on the skin. The size of the localized redness will only be about 3 millimeters, and will usually disappear within a few hours.
Skin testing is generally well tolerated. The most common reaction is local itching and swelling of the test site which resolves within a few hours. Other possible side-effects include itching of the eyes, nose, throat; runny nose, wheezing, light-headedness, hives and nausea. Strongly positive reactions may induce low blood pressure and shock in an extremely rare circumstance. The staff is trained in appropriate management of each of the above possible reactions.
Is the test safe?
Very small amounts of allergens are tested on your skin, so skin testing is safe. During the test, the allergist will watch for a possible severe allergic reaction, but it rarely happens.
What kinds of medications can interfere with results?
Before scheduling a skin test, bring your doctor a list of all of your prescription and over-the-counter medications. Some medications can suppress allergic reactions, preventing the skin testing from giving accurate results. Other medications may increase your risk of developing a severe allergic reaction during a test.
Because medications clear out of your system at different rates, your doctor may ask that you stop taking certain medications for up to 10 days. Medications that can interfere with skin tests include:
Prescription antihistamines, such as hydroxyzine (Vistaril).
Over-the-counter antihistamines, such as loratadine (Claritin, Alavert), diphenhydramine (Benadryl), chlorpheniramine, cetirizine (Zyrtec Allergy) and fexofenadine (Allegra).
Tricyclic antidepressants, such as nortriptyline (Pamelor) and desipramine (Norpramin).
Certain heartburn medications, such as cimetidine (Tagamet) and ranitidine.
The asthma medication omalizumab (Xolair). This medication can disrupt test results for six months or longer even after you quit using it. For comparison, most medications affect results for days to weeks.