People who suspect that they (or their children) have atopic dermatitis should carefully examine skin areas, keeping three questions in mind:
- Is the rash itchy?
- Is there dry skin with a red or scaly rash?
- 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 this disease. 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
A detailed medical history is the most important and reliable tool for diagnosing atopic dermatitis. 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 the disease. 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 diagnosing the condition.
Blood and Skin Tests
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 dermatitis. Even more useful are 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, which is used to rule out other skin diseases, such as a low-grade skin cancer or psoriasis, a doctor first numbs the skin and then removes one or more small pieces of skin. A pathologist then examines the skin sample under a microscope.
- Allergy skin testing: Prick skin tests can be done to common foods or inhalant 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.
Allergy Challenge Tests
If the medical history points to atopic dermatitis, then healthcare providers can move on to specific tests, known as "challenges," to determine if something in the patient's surroundings or in food routinely aggravates the ailment. Patients can then try to avoid these specific triggers.
If a food allergy is suspected, specialists can recommend a food challenge. Patients are "challenged" by being given increasing amounts of food thought to be an allergen and being carefully monitored and observed for any reaction. This is typically done at a specialized testing center.