Diagnosis

Your doctor will ask about your symptoms and may perform a physical exam to find or rule out other medical problems. He or she may also recommend one or both of the following tests:

• Skin test. In this test, your skin is pricked and exposed to small amounts of the proteins found in shellfish. If you're allergic, you'll develop a raised bump (hive) at the test site on your skin.
• Blood test. Also called an allergen-specific IgE antibody test or radioallergosorbent (RAST) test, this test can measure your immune system's response to shellfish proteins by measuring the amount of certain antibodies, known as immunoglobulin E (IgE) antibodies, in your bloodstream.

A history of allergic reactions shortly after exposure to shellfish can be a sign of a shellfish allergy, but allergy testing is the only sure way to tell what's causing your symptoms and to rule out other possibilities, such as food poisoning. Medically supervised food challenges can be performed if any uncertainty remains about the diagnosis.