How you prepare

Before recommending a skin test, your doctor will ask you detailed questions about your medical history, your signs and symptoms, and your usual way of treating them. Your answers can help your doctor determine if allergies run in your family and if an allergic reaction is most likely causing your symptoms. Your doctor may also perform a physical examination to search for additional clues about the cause of your signs and symptoms.

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.