Eczema: Diagnosis and Tests

Have you been asking yourself, "Do I have eczema?" 

People who suspect that they (or their children) have atopic dermatitis should carefully examine skin areas, keeping three questions in mind:

1. Is the rash itchy?
2. Is there dry skin with a red or scaly rash?
3. If the rash has occurred in the past, is the skin thicker in that area?

If the answer to any one of these questions is yes, the next step is to consult a medical specialist--allergist/immunologists or dermatologists know a lot about eczema. They can get an in-depth history and perform additional diagnostic tests, if necessary, including:

• A detailed medical history
• Blood tests and skin biopsy
• Allergy tests

Medical History

A detailed medical history is the most important and reliable tool for diagnosing eczema. An allergist or dermatologist will ask a host of questions, focusing on when the rash appears, where it appears, and how often it does so. They also will ask about itching and other features that characterize atopic dermatitis. Some questions will focus on possible triggers: foods or inhaled allergens, temperature changes, and other features of a person's home or work surroundings that may spark atopic flares.

It is very useful before walking into the doctor's office for patients or parents to write down what they remember about all of these questions. That's because many people have difficulty recalling the information on the spur of the moment in the doctor's office, and accurate answers are key to an eczema diagnosis.

Blood and Skin Tests for Eczema

While the medical history is of paramount importance, additional tests can help support the diagnosis of atopic dermatitis or identify other conditions that may be causing symptoms instead. Some of these tests are:

• Blood tests: These require a small blood sample, typically drawn through a needle in the arm. One such test looks for high levels of eosinophils, cells in the blood that are part of an immune reaction. Another looks for high levels of a molecule called IgE antibody. Blood levels of these are elevated in people with atopic diseases, including eczema. Some patients with eczema also have a food allergy, so your doctor may order allergen-specific IgE tests, which measure levels of the antibody, each of which is associated with a different allergen. Note: measuring IgG antibody to foods is NOT a useful test for determining food allergy.
• Skin biopsy: In this procedure a doctor first numbs the skin and then removes one or more small pieces of skin, which is used to rule out other skin diseases from atopic dermatitis, such as a low-grade skin cancer or psoriasis. A pathologist then examines the skin sample under a microscope.
• Allergy skin testing: If there is concern for an associated food allergy or environmental allergy, prick skin tests can be done to common foods or inhalant/animal allergens to show sensitization or lack of sensitization to specific allergens.
• Patch testing: In this test, small patches covered with allergenic chemicals are placed on the skin for 48 hours, then removed and the skin reaction is evaluated at 72-96 hours. It can identify contact allergy to chemical sensitizers such as fragrances, metals, lanolin, rubber, etc.
• Buccal swabs: The inside of the cheek can be swabbed with a cotton applicator to get cells as a source of DNA material to look for mutations in the Filaggrin gene, one of the causes of eczema.