Allergy laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Laboratory Findings

Allergy testing may be needed to determine if the symptoms are an actual allergy or caused by other problems. For example, eating contaminated food (food poisoning) may cause symptoms similar to food allergies. Some medications (such as aspirin and ampicillin) can produce non-allergic reactions, including rashes. A runny nose or cough may actually be due to an infection.

Skin testing is the most common method of allergy testing. One type of skin testing is the prick test. It involves placing a small amount of the suspected allergy-causing substances on the skin, and then slightly pricking the area so the substance moves under the skin. The skin is closely watched for signs of a reaction, which include swelling and redness. Skin testing may be an option for some young children and infants. Other types of skin tests include patch testing and intradermal testing.

Blood tests can measure the levels of specific allergy-related substances, especially one called immunoglobulin E (IgE). A complete blood count (CBC), specifically the eosinophil white blood cell count, may also help reveal allergies.

In some cases, avoiding certain items to see if one gets better, or using suspected items to see if one feels worse is often used to check for food or medication allergies. This is called "use or elimination testing."

Reaction to physical triggers like applying heat, cold, or other stimulation to body and watching for an allergic response is also tested.

Sometimes, a suspected allergen is dissolved and dropped into the lower eyelid to check for an allergic reaction