Diagnosis of Eczema (Atopic Dermatitis)
Currently, there is no specific test for eczema, and no single symptom or feature can be used to identify the disease. The diagnosis is based on your medical history and the physical exam. Each patient has a unique combination of symptoms, and the symptoms and severity may vary over time.
Your doctor will ask you about your medical history, family history of allergies, your symptoms, and possible exposure to allergens and irritants. Your skin will also be examined for characteristic signs of eczema.
Your doctor may be able to make a diagnosis based on your medical exam. However some tests may be performed to confirm the diagnosis, to check for similar skin conditions, or to look for health problems frequently associated with eczema (such as allergies or hayfever).
These tests may include:
Allergy Skin Test (Skin Scratch/Patch Test)
—This test does not diagnose eczema, but it may be used to determine if you are allergic to specific allergens. A tiny amount of allergen is placed under your skin with a needle in a scratch test or on your skin impregnated into a piece of special tape in a patch test. In most cases, an allergic response is indicated if the skin becomes raised or red within 20 minutes in a scratch test or within 72 hours in a patch test. Since non-allergenic skin irritation is quite common in people who have eczema, these are not entirely accurate tests to diagnose eczema. However, it is useful in identifying your allergens.
—Blood tests are not recommended to diagnose eczema because they have a high rate of false positives and are expensive. However, they may be used to confirm an allergic or atopic tendency by checking the level of IgE, an antibody often present in large quantity in people with allergies and eczema.
—This test is rarely required because diagnosis can almost always be made based on symptoms and medical exam. It might be used in some situations to confirm the diagnosis.
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http://www.niams.nih.gov. Accessed November 25, 2015.