It is estimated that one out of every five Americans suffers from allergies. Determining the substance that is triggering symptoms (the “allergen”) is the key to successful treatment. Allergy testing is the most effective method of accomplishing this.
Skin testing is the preferred method because it is quick, inexpensive and reliable, but blood testing may be an alternative for patients who are unable to tolerate skin testing or those who are taking medications that might interfere with skin test results (such as certain drugs for skin conditions, asthma and heart conditions). Allergy testing is an in-office procedure that is quick and safe. The patient may experience a little discomfort, swelling or itching, but side effects are rare.
The most common type of allergy test is the skin prick test. A drop of solution containing the suspected allergen is placed on the skin of the arm or back. Scratches or pricks are made in the skin with a needle or pin, enabling the allergen to penetrate the surface. A positive reaction is indicated when swelling or redness develops.
An intradermal dilutional test (IDT) is an alternative form of skin testing in which the allergen is injected beneath the skin with a hypodermic syringe. The dosage is gradually increased until a positive result is achieved. Intradermal testing is extremely sensitive and is used for patients who do not test positive with a skin prick test, but that allergen is still believed to be the trigger. It is often used to test for a very specific allergen such as insect venom.
In a skin patch test, a small patch that has been treated with drops containing the suspected allergen is taped to the skin and left in place for a specific period of time (usually 24-72 hours). It is typically used to test for contact dermatitis.
Blood tests work differently; rather than looking for a physical reaction to an allergen, this type of test measures the levels of an antibody known as Immunoglobulin E (IgE) in the blood. This molecule attaches itself to a substance in order to trigger an allergic reaction. The most common blood test is a Radioallergosorbent (RAST) test. It screens for common allergy triggers such as pollen, mold, dust mites and pet dander. High levels of IgE indicate a positive result. RAST is the preferred testing method for infants and children. It is less expensive and results take longer since an outside lab is involved.
