Allergy testing provides valuable insights into what triggers allergic reactions, guiding effective management and treatment. Accurate test results depend heavily on proper preparation, including adjusting certain medications beforehand. Some common drugs can interfere with the body’s natural allergic responses, potentially leading to misleading outcomes.
Why Stopping Medication Matters
Certain medications, particularly antihistamines, work by blocking histamine, a chemical the body releases during an allergic reaction. Allergy skin tests are designed to measure the body’s immediate histamine response to specific allergens. If antihistamines are present in the system, they can suppress this natural reaction, preventing the test from accurately identifying allergens. This suppression can lead to false negative results, where a person might have an allergy that goes undetected. An inaccurate diagnosis can delay appropriate treatment, leaving individuals vulnerable to their allergic triggers.
Medications to Pause and Their Timelines
Several medications must be paused before allergy skin testing for accurate results. Oral antihistamines are a primary concern. Second-generation antihistamines (e.g., loratadine, cetirizine, fexofenadine) require discontinuation for 5 to 7 days before testing. First-generation antihistamines (e.g., diphenhydramine, hydroxyzine) often need to be stopped for 48 hours to 7 days, with some recommendations extending to 10 days for hydroxyzine. These timelines allow the medication to clear from the system, restoring the body’s natural histamine response.
Nasal antihistamine sprays (e.g., azelastine, olopatadine) should be stopped for 1 to 7 days prior to testing. Over-the-counter cold and flu remedies often contain antihistamines; check labels carefully and follow oral antihistamine discontinuation guidelines. H2 blockers (e.g., famotidine, ranitidine), used to reduce stomach acid, have antihistamine properties and need to be paused for 1 to 2 days.
Tricyclic antidepressants (TCAs) like amitriptyline or doxepin can interfere with skin test results due to their antihistamine effects. These may need to be stopped for 1 week or 2 to 3 days before testing. Beta-blockers, used for high blood pressure or heart problems, are not stopped for direct interference. Instead, they can increase allergic reaction severity and make emergency treatment with epinephrine less effective. Discuss discontinuing any prescription medication, including TCAs and beta-blockers, with the prescribing physician before making changes.
What to Take and What to Avoid
While many medications must be paused, several can be continued without affecting allergy test results. Most asthma inhalers (prevention and quick relief) should be continued as prescribed to maintain respiratory health. Nasal steroid sprays (e.g., Flonase, Nasonex) and leukotriene modifiers (e.g., montelukast) do not interfere with skin testing and can be continued. Common pain relievers (e.g., acetaminophen, ibuprofen) are safe to take before testing. Most antibiotics can be continued.
Beyond medications, certain preparations ensure accurate test results. Avoid applying skin creams, lotions, or ointments to the test area for at least 24 hours beforehand. These products could potentially interfere with the skin’s reaction or obscure test sites. Heavy sun exposure to the test area and vigorous exercise that might irritate the skin should be avoided before the appointment. If a dose of a medication that should have been stopped was accidentally taken, contact the allergist’s office immediately for guidance.
Understanding Different Allergy Tests
Stopping medications primarily applies to specific allergy tests. Skin prick tests (SPT) and intradermal tests, which involve introducing small amounts of allergens into or under the skin, are most sensitive to medication interference. These tests rely on the body’s immediate localized histamine response to identify allergens. The presence of antihistamines can prevent the characteristic “wheal and flare” reaction, leading to inaccurate readings.
Conversely, blood tests (IgE antibody tests) measure specific antibodies in the bloodstream. These tests are not affected by antihistamines or other allergy medications because they assess existing antibody levels rather than an immediate skin reaction. This makes blood testing suitable for individuals who cannot safely stop medications. Patch tests, used to diagnose contact dermatitis, involve applying allergens to the skin for an extended period and are not affected by oral allergy medications.