From the Guidelines
The RAST (RadioAllergoSorbent Test) is a blood test that measures the amount of allergen-specific IgE antibodies in the blood, helping to identify specific allergens causing allergic reactions, and is particularly useful when skin testing isn't appropriate, such as for patients with widespread skin disease or those taking medications that interfere with skin tests 1.
Purpose of RAST Testing
The purpose of RAST testing is to detect allergen-specific Immunoglobulin E (IgE) antibodies in the blood, which can help identify specific allergens causing allergic reactions. This test is useful in patients who cannot undergo skin testing, such as those with widespread skin disease or those taking medications that interfere with skin tests.
How RAST Testing Works
RAST testing works by measuring IgE antibodies that the immune system produces in response to specific allergens, such as pollen, foods, pet dander, or insect venom. A healthcare provider will draw a blood sample that is then sent to a laboratory where it's exposed to potential allergens. Results are typically reported on a scale from class 0 (negative) to class 6 (extremely high), with higher numbers indicating greater sensitivity.
Limitations of RAST Testing
While RAST testing is a useful tool for detecting allergen-specific IgE antibodies, it has some limitations. Unlike skin prick tests, RAST doesn't carry the risk of triggering an allergic reaction and doesn't require stopping antihistamines before testing. However, it's generally less sensitive than skin testing, more expensive, and results take longer to obtain, usually several days to a week 1.
Clinical Use of RAST Testing
RAST testing is particularly useful in clinical practice when skin testing is not feasible or when there's concern about severe allergic reactions. It can also be used to monitor the effectiveness of allergen immunotherapy and to identify potential allergens that may be causing symptoms in patients with allergic diseases.
- RAST testing can help identify specific allergens causing allergic reactions
- It is particularly useful when skin testing is not feasible or when there's concern about severe allergic reactions
- RAST testing has some limitations, including being less sensitive than skin testing and more expensive
- It can be used to monitor the effectiveness of allergen immunotherapy and to identify potential allergens that may be causing symptoms in patients with allergic diseases 1
From the Research
Purpose of the RadioAllergoSorbent Test (RAST)
The RadioAllergoSorbent Test (RAST) is a diagnostic tool used to detect allergen-specific Immunoglobulin E (IgE) antibodies in the blood. The main purpose of RAST is to:
- Aid in the diagnosis and management of human allergic (IgE-dependent) diseases 2
- Detect specific IgE antibodies to approximately 15 allergens that evoke a large majority of aeroallergen or food-related allergic disorders 2
- Diagnose type I hypersensitivity reactions to foods or reactivity to aeroallergens in patients with relative contraindications to skin-prick testing 3
Mechanism of RAST
The RAST involves:
- Binding of antigen (allergen) to a solid phase, such as a paper disk 3
- Incubation with human serum to detect bound IgE antibodies 3
- Use of radiolabeled anti-human IgE to detect bound IgE antibodies 3
- Reporting of results in arbitrary units of IgE per milliliter of serum 3
Advantages and Applications of RAST
RAST is a valuable aid in the diagnosis of allergies, being non-burdensome and risk-free 4. It is used to: