In order to treat allergies, patients must be tested to determine the allergen that is causing their symptoms. Allergy testing may involve the skin or blood.
Intradermal Dilutional Testing (IDT) is an alternative form of skin testing in which a tiny amount of allergen is injected beneath the skin with a hypodermic syringe. The dosage is increased in the hope of achieving a positive reaction. IDT testing is highly sensitive, and is useful as a first line testing option for patients.
A radioallergosorbent test (RAST) is a blood test used to determine the substances responsible for an allergic reaction. Blood tests differ from skin tests; instead of determining an allergy based on a skin reaction, these measure antibody levels in the bloodstream. They are not as sensitive as skin testing and therefore less reliable, but a useful alternative for patients who cannot tolerate skin testing.