Allergy skin testing identifies specific substances that trigger allergic reactions, such as environmental allergens or certain foods. Accurate identification of these allergens is important for developing an effective management plan for allergic conditions.
Recommended Discontinuation Period
Healthcare providers recommend stopping antihistamines several days before a skin prick test. The discontinuation period for oral antihistamines ranges from 3 to 7 days. Long-acting antihistamines, such as cetirizine, levocetirizine, loratadine, and fexofenadine, require a 5-day discontinuation period. Shorter-acting antihistamines may only need 48 hours.
This period allows the body to clear the medication from its system. Antihistamines block the body’s natural allergic response. Clearing these medications ensures the skin reacts truthfully to allergens, preventing false-negative results. Always consult your allergist for precise instructions tailored to individual circumstances and medications.
How Antihistamines Affect Skin Testing
Antihistamines interfere with skin tests by blocking histamine receptors. When exposed to an allergen, the immune system releases histamine, a chemical causing allergic reactions like itching, redness, and swelling. During a skin prick test, small amounts of suspected allergens are introduced into the skin to observe this response.
If antihistamines are present, they prevent histamine from binding to its receptors, suppressing the natural skin reaction. This suppression can lead to false-negative results. Inaccurate results could delay proper diagnosis and effective treatment for allergic conditions.
Managing Allergy Symptoms During Discontinuation
Managing allergy symptoms during antihistamine discontinuation can be challenging. Non-pharmacological approaches offer relief without affecting test results. Saline nasal rinses clear mucus and allergens from nasal passages. A neti pot or squeeze bottle with distilled or sterile water can relieve congestion and irritation.
Allergen avoidance is another strategy; keeping windows closed, using high-efficiency particulate air (HEPA) filters, and showering before bed can reduce exposure to airborne triggers. Cold compresses soothe itchy eyes. While oral antihistamines must be stopped, alternatives like nasal steroid sprays (e.g., Flonase, Nasacort) and leukotriene modifiers (e.g., montelukast) do not interfere with skin tests and can be continued. Always confirm this with your doctor.
Medications to Discontinue Before Testing
Beyond common oral antihistamines, other medications contain antihistamine components and must be stopped before allergy skin testing. These include over-the-counter cold and flu remedies (e.g., diphenhydramine, chlorpheniramine) and sleep aids (e.g., Tylenol PM, Advil PM, Unisom, Nyquil, containing diphenhydramine or doxylamine).
Anti-nausea medications like promethazine also have antihistamine effects. Additionally, certain heartburn medications, specifically H2 blockers like cimetidine (Tagamet), famotidine (Pepcid), and ranitidine (Zantac), can suppress skin reactions. Carefully read medication labels and provide your allergist with a complete list of all prescription medications, over-the-counter drugs, supplements, and herbal remedies to ensure accurate test results.