How are food allergies diagnosed?
Your doctor can perform a skin test to determine which substances cause a reaction. The skin test involves applying a small amount of an allergen (allergy-causing substance) and then making either a tiny scratch or small prick with a needle in your arm or back. The scratches that become red and itchy indicate which substances trigger a defensive response by your immune system.
Your doctor might also do a radioallergosorbent blood test (RAST) to check the number of antibodies produced by the immune system. Elevated levels of certain antibodies can identify particular food allergies. Also, if you maintain a food diary, your doctor will have a much better starting point when determining your allergy-triggering foods.