Allergy Diagnosis

Allergy testing is the only way to find out if you’re allergic. It is also the only way to find out which allergens are causing your allergic condition. Once you know what you are allergic to, it is much easier to avoid your allergens and treat your symptoms.

How are allergies diagnosed?

First, your doctor will ask you questions about your health and symptoms. Make sure to tell your doctor if anyone in your family has allergies. If family members have allergies, your chances of having allergies increase. Your doctor uses the following information to make a diagnosis of allergy:

• Physical exam
• History of your symptoms and family history
• Allergy tests (not always needed)

Learn how to prepare yourself for what the doctor might ask you about your medical history.

Allergy tests can be done to help identify if you are allergic and what you are allergic to. Once allergies are identified, specific avoidance and treatment measures can be recommended. There are several types of allergy testing.

What types of allergy testing can be done?

Prick Skin Testing

A reliable test for allergies is the prick skin test. A small amount of each thing you may be allergic to (allergen) is placed on the skin - often the back. The skin is then pricked. If you are allergic to an allergen, you will get a bump and redness where the skin is pricked. After a short time, each skin test reaction is measured for swelling and redness. If there is a large enough skin reaction, it means that you may be allergic to the allergen placed at that site. The information from your prick skin test results and your history of symptoms will help your doctor to determine if you have an allergy.

Antihistamines can affect the skin test results. Your doctor may tell you to stop these medications for days to weeks before the testing is done. Other medicines can also affect the results and may need to be avoided. Ask your healthcare provider what medicines to avoid before your prick skin tests are done.

Learn more about prick skin testing.

Intradermal Skin Testing

Another form of skin testing for allergy is by intradermal skin testing. This method is not as reliable as prick skin testing. It is most often used when prick skin testing is negative and there is a strong suspicion of allergy from the history. A small amount of each thing you may be allergic to (allergen) is placed under the skin with a needle, usually on the arm. If you are allergic to an allergen, you will get a bump and redness where the needle has gone under the skin. After a short time, each skin test reaction is measured for swelling and redness. If there is a large enough skin reaction, it means that you may be allergic to the allergen placed at that site. The information from these test results and your history of symptoms will help your doctor to determine if you have an allergy.

Antihistamines and other medicines can also affect these skin test results. Ask your healthcare provider what medicines to avoid before your skin tests are done.

Learn more about intradermal skin testing.

Blood Testing

A blood test is another kind of test that can be done to help find out if you have allergies. There is some evidence that blood tests are not as sensitive as prick skin tests in determining allergies. However, a blood test may be done if you have skin problems or, if there is concern that someone will have a severe reaction to a skin test (this is very rare). There are many types of blood tests that can be used to detect allergies. The most common one is called RAST testing.

Learn more about RAST testing and if it’s right for you.

Patch Skin Testing

Patch skin testing may be used to find out if a rash is from direct contact with an allergen. Small amounts of allergens are placed on the skin, often the back. The skin is covered with a watertight bandage for several days. After several days the patch is removed and the skin reactions are measured to find out if you may have a contact allergy.

Food Challenge

If you have a positive skin test to foods, your doctor may consider a food challenge. In some cases, this test is the only way to make a diagnosis of food allergy. Increasing doses of the suspected food are given and you are checked for symptoms. The food challenge may be double blind. This means neither the patient, nor the person giving the test knows the type of food being challenged. Only the doctor prescribing the challenge knows the food. Food challenges are done in a medical setting where emergency care is available. This test is rarely done if there is a history of a life-threatening reaction to a food.

• What is a food challenge?
  Research has shown that many people unnecessarily restrict their diets because they mistakenly think they are allergic to certain foods. Dan Atkins, MD, describes how food challenges are conducted.
  
• Food challenges: why bother?
  Dan Atkins, MD, outlines why food challenges are such a useful tool.

Alternative Methods

There are many other tests to diagnose allergies. Many have not been scientifically proven to be effective and accurate. Talk with your doctor or a board-certified allergist about the best way to determine your allergies.

Learn more about alternative methods of allergy testing.

Should you see an allergy expert?

Many people with allergies see a family doctor for allergy care. You may choose to visit a doctor who is an expert in allergies. These doctors are called board-certified allergists. Here are a few reasons to see an allergy expert:

• Your symptoms make daily activities hard.
• Your symptoms are getting worse.
• You are concerned about side effects of medicine.
• Your regular doctor refers you to an expert for tests.

Allergy tests can be done to help identify if you are allergic, and what you are allergic to. Once allergies are identified, specific avoidance and treatment measures can be recommended. Talk with you doctor if you think you may have allergies.

What is the role of National Jewish Health?

For many years, National Jewish Health scientists have made important contributions to our understanding of allergy, and the best means to diagnose and treat it. For example, in 1965 National Jewish Health researchers discovered the IgE antibody - the molecule linked to allergy. This finding revolutionized diagnosis and patient care. In 1973, Dr. Charles May devised the double-blind food allergy challenge, an objective evaluation of adverse reactions to food. This test is now the "gold standard" for diagnosing food allergy, a method adopted worldwide.

Today, National Jewish Health remains an international leader in allergy research and treatment. Along with patient volunteers, our scientists evaluate new methods of allergy testing, and new medications for allergy treatment.

In the laboratory, researchers work to understand the molecular and cellular activities that take place during allergic and inflammatory reactions, and then seek ways to regulate those responses by using the body's own array of chemicals.

In the clinic, some of the nation’s best doctors work with patients to help alleviate and manage allergy symptoms. At National Jewish Health, we believe in a multidisciplinary approach to disease management. The best way to treat disease and improve quality of life is as a team that includes the researcher, the clinician and the patient.

This information has been approved by David Tinkelman, M.D. (January 2005).