The sneezing, itchy eyes and runny nose that accompanies allergies can be extremely frustrating. Skin prick testing is one way to diagnose allergies and to determine the specific allergen to which the patient is reacting. This test is performed by scratching the surface of the skin with a small amount of allergen and measuring the skin reaction. While this testing is useful in allergy diagnosis, several medications can interfere with testing and need to be stopped prior to the clinic visit.
Antihistamines
Both prescription and over-the-counter antihistamines must be stopped prior to skin testing. Antihistamines block the effects of histamine and are used for treating allergic reactions. Since histamine is the chemical that causes the skin response to an allergy test, antihistamines cannot be used prior to skin testing. Some examples of antihistamines include Claritin, Benadryl, Zyrtec and Allegra. Antihistamines should be stopped five days prior to skin testing and a physician can help determine whether a medication falls into this category.
Antidepressants
Some antidepressants, particularly of the class known as tricyclic antidepressants, can interfere with skin testing. Tricyclic antidepressants are often used to treat major depression and sometimes used to treat pain disorders. These medications prevent the reabsorption of the chemicals serotonin and norepinephrine in the brain and were among the first medications developed to treat depression. While these medications do interfere with skin testing, a patient should not discontinue them without discussing this with a physician.
Heartburn Medications
Heartburn medications known as H2-blockers interfere with skin testing as well. These medications decrease the amount of acid made in the stomach by blocking the histamine receptors in the gut and prevent heartburn in this manner. H2-blockers, such as ranitidine and cimetidine, are sometimes used to treat allergic reactions and may interfere with histamine response in the skin, rendering allergy skin testing uninterpretable.
Other Options
If medications cannot be stopped prior to allergy testing, blood testing can be performed instead of skin prick testing. While blood testing may yield more false positives, it is a reliable substitution in a patient who is unable to come off of medications or who has severe skin disease.
