What Tests Are Used to Diagnose Atopic Dermatitis?
Sometimes in the process of making a diagnosis of atopic dermatitis (AD), a doctor will order tests. The most common tests that are run are allergy tests, as people with AD have a higher risk of developing allergies, and allergens can act as a trigger for AD.
Allergy progression and the "atopic march"
Doctors have coined the term “atopic march” to describe the progression of allergic diseases that is frequently seen in people who have atopic dermatitis in childhood and who later develop these other allergic conditions. Some people who have AD in childhood outgrow the disease, and it goes into remission. Scientists do not understand the mechanisms behind outgrowing the condition but believe it may have both genetic and environmental factors.1
The word “atopy” means a genetic disposition to develop an allergic reaction and produce elevated levels of immunoglobulin E (IgE) when exposed to an environmental allergen. Immunoglobulin is a type of protein that is part of the immune system and that acts as an antibody to attach and destroy foreign substances. There are five different types of immunoglobulin, and the IgE protein is found in increased levels in people with allergy. IgE causes the body to release histamine when it comes into contact with an allergen. Approximately 80% of people with AD have elevated IgE levels, but having elevated IgE levels is not necessary nor sufficient to make the diagnosis of AD.2-4
Common allergies with atopic dermatitis
AD puts a person at a higher risk of developing hay fever, or allergic rhinitis. Its symptoms include runny and/or stuffy nose, sneezing, fatigue, and itchy eyes, mouth, or skin. Hay fever may be seasonal, with a flare in symptoms due to allergic sensitivity to airborne mold spores or pollens, or perennial, with symptoms year-round due to sensitivity to pet dander, mold, dust mites, or cockroaches.1,5
People with AD are at a higher risk of developing food allergies, particularly those who develop AD as a child. A person with a food allergy has a rapid reaction (within 30 minutes of exposure) to a particular food. Symptoms may include hives and itching of the lips. A severe reaction includes respiratory, gastrointestinal or anaphylaxis (an acute allergic reaction that requires immediate medical attention as it can lead to severe swelling of airways, lowered blood pressure, or shock). The most common food allergies that worsen AD include cow’s milk, eggs, fish, peanuts, soy, tree nuts, and wheat.6,7
People with AD are also at an increased risk of developing asthma, a chronic condition of the lungs that involves inflammation of the airways after exposure to a trigger. Asthma makes it difficult to get air in and out of the lungs and can cause symptoms such as wheezing, coughing, shortness of breath, and tightness of the chest.5,6
People with AD that have symptoms of allergies or whose AD is persistent or difficult to treat may receive additional testing for allergens. Tests for allergens include skin prick testing, patch testing, and blood tests.8,9
Skin prick testing
Skin prick testing involves applying a diluted allergen with a prick or puncture on the surface of the skin. The skin is observed for approximately 15 minutes to see if a reaction develops. A positive reaction to the allergen is a “wheal,” a raised, red bump and a surrounding “flare,” of area of redness.1
Patch tests use patches containing allergens that are placed on the skin and worn for 48 hours. Patch tests can be helpful to detect allergic contact dermatitis, which causes a delayed allergic reaction of the skin.9Blood testsBlood tests involve testing for allergen specific IgE. Negative test results can be helpful to rule out specific allergies, like foods, but positive test results only identify sensitization and require additional information to confirm whether they are clinically relevant.8Food allergy evaluationThe American Academy of Dermatology recommends children less than 5 years of age with moderate to severe AD should be considered for food allergy evaluation if they have persistent AD in spite of topical treatment and proper skin care management or if they have a history of an immediate reaction after ingesting a specific food.6,7Another alternative for testing for food allergies is food elimination diets, however, excessively restrictive diets can lead to weight loss, poor growth, calcium deficiency, and other complications in children. People considering food elimination diets should talk with their doctor.8