Testing can verify allergy to shellfish

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.

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.