Allergies: Two Types of Testing

Allergies are a chronic problem for millions of Americans. The key to successful treatment is determining which allergens are responsible for triggering your symptoms. To accomplish this, your doctor will administer allergy testing.

Allergy Testing: Skin v. Blood

There are two types of allergy tests commonly used: skin tests and blood tests. Each has their pros and cons, but skin tests are preferred by most doctors as they are safe, inexpensive and provide the most reliable results.

Three methods of skin testing exist. In a skin prick test, a drop of the suspected allergen is placed somewhere on the skin (typically the arm or back). A scratch is made in the skin, allowing the allergen to penetrate. If any redness or swelling develops, the results are considered positive. In an intradermal test, the allergen is injected directly into the skin. This type of test is usually reserved for testing a very specific allergen such as insect venom, and used when results from the skin prick test are inconclusive but the allergen tested is still believed to be responsible for the symptoms. A skin patch test utilizes a small patch that has been treated with drops of the suspected allergen; this is taped to the skin and left in place for 24-72 hours. It’s used to test for contact dermatitis specifically.

Allergy skin testing rarely causes discomfort or complications. There may be a little redness, swelling and itching, but this typically subsides quickly. In extremely rare cases, severe allergic reactions can occur immediately.

Patients who cannot tolerate skin testing may be given blood tests. These are less reliable than skin tests because they don’t show a physical reaction. Instead, an allergen is introduced into the bloodstream, and the antibody levels produced by the body are measured. An increase in antibodies is usually indicative of an allergic response.

If a food or drug allergy is suspected, “use or elimination testing” may be recommended. This involves avoiding, or alternately using, suspected triggers to see if they cause a reaction.

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