Allergy testing identifies specific substances, known as allergens, that trigger an immune system response. When the immune system mistakenly identifies a harmless substance as a threat, it produces Immunoglobulin E (IgE) antibodies, which cause allergic reactions. The purpose of testing is to pinpoint these triggers, allowing a physician to create an effective management plan. This diagnostic tool confirms a suspected allergy, which is necessary before starting specialized treatments like immunotherapy.
When Initial Testing Is Necessary
Initial allergy testing is warranted when a person experiences persistent or recurring symptoms suggesting an allergic reaction rather than a temporary illness. Indicators often include chronic nasal congestion, sneezing, itchy and watery eyes, or seasonal symptoms not relieved by over-the-counter medications. Testing is especially important for individuals with asthma, as identifying triggers like dust mites or pet dander can significantly improve respiratory control.
Testing is also recommended following a severe, localized reaction, such as large swelling from an insect sting, or any history of anaphylaxis. Anaphylaxis is a severe, whole-body allergic reaction that affects breathing and blood pressure, making accurate trigger identification important for safety. For suspected food allergies, repeated instances of hives, vomiting, or abdominal cramping after eating a specific item signal that diagnostic testing is needed to confirm the cause and guide safe dietary avoidance.
Common Methods of Allergy Testing
The two most common methods used to diagnose immediate-type allergies are the Skin Prick Test (SPT) and the Specific IgE Blood Test. The SPT is usually the first line of investigation because it is quick, relatively painless, and provides results within 15 to 20 minutes. During an SPT, a small amount of liquid allergen extract is placed on the skin, typically the forearm or back, and the area is lightly pricked. A positive result is a raised, red, itchy bump, similar to a mosquito bite, which confirms the presence of specific IgE antibodies.
The Specific IgE Blood Test serves as an alternative when skin testing is not feasible, such as for patients taking interfering medications or those with severe skin conditions like widespread eczema. This test involves drawing a blood sample, which is analyzed in a laboratory to measure the concentration of IgE antibodies against specific allergens. While the blood test provides quantitative IgE levels useful for monitoring, the results are not immediate and often take several days. The physician determines the most appropriate test based on the patient’s circumstances and medical history.
Guidelines for Allergy Re-Testing Frequency
The frequency of re-testing depends on the individual’s age, allergy type, and treatment plan, as allergies are dynamic and can change over a lifetime. For adults with stable environmental allergies, re-testing every two years is a reasonable guideline, especially if symptoms have returned or worsened despite avoidance and medication plans. Periodic re-evaluation is necessary because the body can develop new sensitivities or existing allergies can increase in severity, requiring an updated treatment strategy.
For patients undergoing allergen immunotherapy, which builds tolerance to allergens, re-testing is often integrated into the treatment timeline. Although the full course of therapy typically lasts three to five years, the patient’s response and progress are assessed by the allergist at least every 12 months. The decision to stop or extend treatment after the initial period is individualized, based on sustained symptom relief.
In pediatric patients, re-testing is often more frequent, particularly for food allergies children commonly outgrow, such as milk, egg, soy, and wheat. To track the natural resolution of these sensitivities, an allergist may recommend repeat testing every 6 to 12 months during the first few years of life. If initial test results were highly positive, indicating a stronger reaction, the re-testing interval might be extended to every two to three years, depending on the specific food allergen.
Any significant change in a person’s allergic status necessitates a re-test, regardless of age or routine schedule. This includes the sudden onset of new symptoms, an unexpected severe reaction, or a move to a new geographic region introducing different local pollens, molds, or environmental allergens. Retesting is also required before attempting an oral food challenge, the procedure used to definitively confirm if an allergy has been outgrown.