Which allergy test measures levels of antibodies after exposing a blood smear to suspected allergens?

The RAST test, or Radioallergosorbent Test, is a specific assay that measures the levels of specific IgE antibodies in the blood following exposure to suspected allergens. In this test, a blood sample is obtained from the patient and is exposed to purified allergen extracts. If the patient has an allergy to a particular allergen, the IgE antibodies in the blood will bind to the allergen. The bound antibodies can then be quantified, providing information on the presence and level of the allergic response. This test is particularly useful because it is less invasive than skin tests and can be performed on patients who may have contraindications for skin testing, such as those with extensive dermatological conditions or those on antihistamines.

In contrast, other tests, such as the skin prick test and the intracutaneous test, involve direct exposure of the skin to allergens and measure immediate reactions rather than measuring antibody levels in the blood. The patch test is used primarily for diagnosing delayed-type hypersensitivity reactions and also does not measure antibodies but rather examines skin reactions after prolonged exposure to a suspected allergen. This distinction is important to understand the RAST test’s role in allergy diagnostics.