Allergy Diagnosis

Learn the right questions to ask your allergist and how an allergy test is performed

Taking the first step

By now you probably suspect you, a family member or a friend has an allergy. To get a diagnosis, you should consult with your physician or an allergist/immunologist, a physician specially trained in this area.

While there are many over-the-counter medications available, they are not without side effects, particularly in long-term use. Find out what exactly you are allergic to so that the least potent, but still effective, medication can be used. Self-prescribing can become dangerous, particularly if you take more than one substance, as interactions are possible. Just because you can buy medication without a prescription doesn’t mean it is harmless.

In choosing an allergist, speak to your primary health care provider for a referral, as well as friends and family members who may be able to suggest a physician. The same name may come up.

Before having the consultation, arm yourself with information. Keep a diary of symptoms to give the allergist as much information as possible. Write down any questions you may have before the visit and bring the list with you. Also, take notes during your visit so that you don’t have to try to remember everything that was discussed.

The allergist will want to take a full history. Questions asked may include: What are your symptoms? How long have they been going on? Is there a family history of allergies? What makes the symptoms better? What makes them worse? Are you taking any medication now? Other than allergy medication, what other medications do you take?

If you suspect a food allergy, the allergist may suggest an elimination diet, in which certain suspect foods are eliminated from your diet for a period of time, perhaps a few weeks. Then, one at a time those foods will be re-introduced. You will be asked to pay close attention to any symptoms you experience during the re-introduction period. Offending foods may then be withdrawn again, to see if the symptoms clear up.


Allergy testing is usually done by either a skin test or a blood test.

Skin testing

In the skin test, a small dose of the suspected culprit is injected just under the skin, or scratched into the skin. When there are several suspected allergens, a “grid” format may be used so that it is clear which allergen is being placed where. The back, or the back of the arm, may be used for the test, depending on the number of allergens being tested. The allergist will check the site to see if there is a local reaction, such as redness, itching, or raised bumps or welts. The allergist also may measure the area to see how large the reaction is.

If the physician suspects the possibility of an anaphylactic reaction, based on the history taken, that particular substance may not even be tested. Before undergoing the skin test, ask your physician how the office is prepared to handle anaphylaxis, should it occur. Is there emergency epinephrine and oxygen readily available? Is the staff trained in using the equipment? Is the doctor’s office in a hospital with an emergency department? How long would it take to get to an emergency department if needed? While anaphylaxis is rare, when it does occur, you need to get the proper help immediately.

Blood testing

Your physician may decide to administer a blood test called the radioallergosorbent test (RAST), instead of skin testing. In this case, blood is drawn from a vein and then sent for testing for the presence of allergen-specific antibodies. It is possible to have a positive blood test without symptoms. This is another reason why a thorough history is taken. The diagnosis of an allergy will be made based on all the information gathered. The RAST is not considered to be as sensitive as the scratch skin test.