DEAR DOCTOR K:

I've always loved shellfish. But lately when I eat it, I break out in hives. Could I be allergic?

DEAR READER:

You sure could be. Such an allergy could cause more symptoms than just a rash, including low blood pressure and difficulty breathing, so you need to find out if you are allergic to shellfish. See an allergist, a doctor who specializes in diagnosing and treating allergies.

Before your appointment, put together a description of your symptoms and the situations that triggered them. For example, are there foods other than shellfish you might be allergic to? Are there any other things that cause a rash -- medicines, skin creams or deodorants, exposure to particular animals or plants? Jot down what you think are the likely allergens.

Once you and your allergist agree on a list of suspects, it's time for allergy testing.

Testing usually begins with a skin prick test. This is safe, easy and inexpensive, and the results are apparent within minutes.

For this test, your doctor will puncture the skin on your forearm. He or she will then put a small amount of the allergen being tested onto the puncture site. If an allergic reaction is triggered, you'll have an itchy, swollen, red spot on your forearm within 15 minutes.

Several types of blood test are sometimes used as alternatives to a skin prick test, although they aren't as reliable. One test measures levels of specific antibodies to the suspected food. A certain amount of antibodies indicates an allergy.

But interpreting a positive blood or skin test is not as straightforward as you might think. Even a positive test doesn't prove that you will have a reaction if you consume the food.

A more reliable test is a food challenge. You eat small amounts of a suspected food until you begin to have an allergic reaction. If you can eat a normal serving without consequences, the doctor can rule out an allergy to that food.

Food challenges should always be done by experienced clinicians in medical facilities that can treat life-threatening allergic reactions.

We have more information on food allergies in our Special Health Report, "Food Allergy, Intolerance and Sensitivity." You can find out more about it at my website.

Until you get tested for a shellfish allergy, avoid eating shellfish -- no matter how tempting it may be.

(Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.)

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