Allergy testing helps diagnose and manage the immune system’s reactions to typically harmless substances. This testing is often necessary for parents seeking answers about a child’s chronic symptoms, such as persistent rashes, unexplained stomach issues, or respiratory distress. Identifying specific allergens—whether foods, pollens, or pet dander—allows for the development of a precise management plan. Understanding the testing process provides a clear path forward for the child’s health.
Preparing the Child for Allergy Testing
Physical preparation involves temporarily stopping certain medications that can interfere with test accuracy. Antihistamines, which block the allergic response, must be paused before a skin test. For most long-acting, non-sedating antihistamines, this washout period is typically five days, while shorter-acting ones may require a 48-hour pause.
Parents must also discuss other medications with the physician, as some cold remedies, decongestants, and certain antidepressants can suppress the reaction. Parents should ensure the child wears loose, comfortable clothing, preferably short sleeves, to allow easy access to the forearm or back for the procedure.
Emotional preparation ensures a smooth experience. Parents should explain the process using simple, age-appropriate language, reassuring the child that the test involves minor, quick discomfort. Bringing a favorite toy, book, or electronic device can provide a helpful distraction during the testing and the subsequent waiting period.
The Skin Prick Test Procedure
The skin prick test, or scratch test, is the most common diagnostic tool used for identifying immediate-type allergies in children. The test is conducted on the forearm or upper back, which provide large, easily accessible surfaces. The clinician first cleans the skin and then marks small spots, corresponding to the specific allergens being tested.
A tiny drop of a liquid allergen extract is placed on each marked spot, often alongside two control solutions. One control is saline (no reaction), and the other is histamine (causes a bump to confirm skin reactivity). Using a sterile lancet, the clinician gently pricks the top layer of skin through the drop of extract. This action is a light scratch, briefly introducing the allergen below the surface.
The child then waits quietly for approximately 15 to 20 minutes for a reaction to develop. If allergic, immune cells release histamine at the site. This causes a localized inflammatory response: a small, raised, itchy bump called a wheal, surrounded by redness known as a flare. The clinician then measures the diameter of the wheal and flare to record the test results.
Secondary Allergy Testing Methods
When the skin prick test is inconclusive, cannot be performed, or carries too great a risk, alternative methods are used to confirm a diagnosis. The specific IgE blood test (sometimes called RAST or ImmunoCAP) measures the amount of allergen-specific IgE antibodies in the blood. This method is often preferred for children with severe, widespread eczema, which makes skin testing unreliable, or for those who cannot safely stop taking necessary antihistamine medications.
A blood sample is drawn and sent to a laboratory, where the IgE levels specific to various allergens are quantified, with results typically available after several days. Unlike skin tests, the IgE blood test is not affected by medication, but it only indicates immune sensitization and does not provide an immediate answer.
The Oral Food Challenge (OFC) is considered the most definitive method for diagnosing a food allergy. This procedure is conducted only in a controlled medical setting (clinic or hospital) under physician supervision, as they can manage a potential severe reaction. The child consumes gradually increasing, measured amounts of the suspected food over several hours.
Medical staff closely monitor the child for any signs of an allergic reaction throughout the challenge and for a period afterward. The OFC is used to confirm a suspected allergy when other tests are ambiguous or to determine if a child has outgrown a known food allergy. If a reaction occurs, the challenge is immediately stopped, and treatment is administered.
Interpreting the Results and Next Steps
Interpreting allergy test results involves more than noting a positive or negative reaction. A positive skin test result, indicated by a wheal size of three millimeters or more greater than the negative control, suggests the child is sensitized to that allergen. However, sensitization only means the body has produced IgE antibodies against the substance and does not automatically confirm a clinical allergy.
The physician integrates test results with the child’s medical history and reported symptoms to make a definitive diagnosis. It is common for allergy testing to show a positive result to a substance that the child tolerates without any reaction, highlighting the importance of this clinical correlation.
Once a diagnosis is confirmed, the physician establishes a comprehensive management strategy with the family. This plan typically involves advice on strict allergen avoidance and education on recognizing early symptoms of a reaction. For children diagnosed with a severe allergy, the physician will prescribe and train the parents on the use of an epinephrine auto-injector, creating a formal Allergy Action Plan for emergencies.