RAST

Radioallergosorbent Test (RAST) is a blood test used to determine to what substances a person is allergic. This test is especially useful for individuals who cannot undergo skin prick tests, such as those with extensive eczema, taking medications that interfere with testing, or are too sensitive to allergens to risk a skin test.

Overview

The RAST measures the amount of Immunoglobulin E (IgE) antibodies to specific allergens in the blood. When a person with an allergic disposition is exposed to a specific allergen, their immune system produces IgE antibodies against that allergen. By measuring these antibodies, healthcare providers can identify the allergens causing an allergic reaction in a patient.

Procedure

During the RAST, a healthcare provider draws a blood sample from the patient. This sample is then sent to a laboratory, where it is exposed to various known allergens attached to a solid phase. If the patient's blood contains IgE antibodies to any of these allergens, they will bind together. A secondary antibody, labeled with a radioactive marker or an enzyme, is added to measure the bound IgE- allergen complexes. The amount of secondary antibody that binds correlates with the level of IgE antibodies in the patient's blood, indicating their sensitivity to specific allergens.

Advantages and Disadvantages

One of the main advantages of the RAST is its ability to test for allergies without exposing the patient to potential allergens, making it safer for those with severe allergies. It is also beneficial for patients who cannot stop taking antihistamines or other medications that interfere with skin testing.

However, RAST is generally more expensive than skin prick tests and may not be as sensitive in detecting allergies to some substances. Additionally, the results take longer to obtain, usually several days to a week.

Comparison with Other Tests

The RAST has largely been replaced by more modern tests, such as the ImmunoCAP Specific IgE blood test, which offers greater sensitivity and specificity. However, the term "RAST" is still commonly used by the general public to refer to any form of blood test for allergies.

Applications

RAST is used to diagnose allergies to a wide range of substances, including food allergies, drug allergies, insect venom allergies, and environmental allergies. It is particularly useful in cases where skin testing is not possible or practical.

See Also

• Allergy
• Allergen
• Immunoglobulin E (IgE)
• Skin prick test
• ImmunoCAP Specific IgE blood test