Which antigen does the RAST test measure?

The RAST (RadioAllergoSorbent Test) is a specific blood test that measures the amount of immunoglobulin E (IgE) antibodies in response to specific allergens. When a person is exposed to an allergen, their immune system may respond by producing IgE antibodies specific to that allergen. These IgE antibodies play a crucial role in allergic reactions, triggering the release of histamines and other chemicals from mast cells that result in allergy symptoms.

Because the RAST test specifically quantifies IgE levels, it is particularly useful in diagnosing allergies and assessing an individual's sensitivity to a wide range of allergens. The presence of elevated IgE levels can indicate an allergic condition, making it a valuable tool for medical professionals in identifying allergies in patients.

The other immunoglobulin types mentioned—IgA, IgM, and IgG—serve different functions in the immune response but are not the focus of the RAST test. IgA is primarily involved in mucosal immunity, IgM responds initially to infections, and IgG is the most abundant type in the bloodstream, providing long-term immunity. None of these immunoglobulins are specifically measured by the RAST test, making IgE the correct answer.