Table of ContentsView AllTable of ContentsWhat Is a RAST Test?RAST Tests vs. Skin TestsWhat Can RAST Test For?How It’s PerformedAccuracyResultsConsiderations
Table of ContentsView All
View All
Table of Contents
What Is a RAST Test?
RAST Tests vs. Skin Tests
What Can RAST Test For?
How It’s Performed
Accuracy
Results
Considerations
A RAST test (radioallergosorbenttest) is a blood test used to check for allergies. It measures your immune system’s reaction to certain exposures (such asfood allergens) and the responses that lead to allergy symptoms.
Many healthcare providers use skin tests to screen for theseimmunoglobulin E (IgE) antibodyresponses in your blood. That’s because RAST and other blood allergy tests (like ImmunoCAP) are less reliable screening tests.However, RAST can be an alternative to a skin prick in some cases, as with children who don’t tolerate skin tests well.
This article explains how the RAST test is performed, along with its limitations. It also discusses how to read a RAST test and what the values on your test may indicate.
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RAST stands for radioallergosorbent test. It may be used instead of skin tests to detect a food allergy in specific groups, including people with severeeczemaand those who need to stay onantihistaminemedications.
RAST also can be used to monitor IgE levels in people who already have a food allergy diagnosis.
Besides RAST, other blood tests for allergies include the enzyme-linked immunosorbent assay (ELISA) orfluorescent enzyme immunoassay(FEIA) tests. The ImmunoCAP test is a preferred method, allowing for molecular-level diagnosis in support of more targeted treatment options.
In the United States, the National Institute of Allergy and Infectious Diseases (NIAID) has recommended that more sensitive tests be preferred instead of RAST when diagnosing allergies.The ELISA tests are especially useful for testing food allergies.
What Types of Allergy Tests Are Available?
A number of skin tests may be used to diagnose an allergy, rather than relying on the RAST test.
Allergy Skin Tests
Skin tests include:
If a skin test is positive, you’ll find a red, raised area where reaction to the allergen occurred.
Your healthcare provider will choose a test based on the suspicion of a certain type of food or other allergy. That decision will be based, in part, on your overall health history, your symptoms, and the findings of their physical examination.
RAST Tests for Allergies
RAST tests are used for many of the same reasons that skin prick tests are. The allergy blood tests in general are considered to be comparably effective as the skin pricks are for food and airborne (respiratory) allergies. But they should be used alongside of the intradermal test when evaluating an allergy to medication or an insect venom (likebee stings).
RAST and other blood tests may be better than skin tests if:
Keep in mind that not all tests are used for the same types of allergic reactions. For example, the skin prick test typically is used to diagnose allergies to food, medication, or environmental irritants such aspollen. Skin prick tests tend to be less expensive than blood tests. (Your costs will depend on your insurance coverage.) However, they also test for fewer allergens than blood tests.
How Can You Find Out If You’re Allergic to a Medication Before You Take It?
Blood tests like the RAST test can be used to test for a number of allergen types, including:
The RAST test also can help when diagnosing people with asthma symptoms, due to the strong link between allergies and asthma in both children and adults.Tests may be geared toward irritants that you inhale, like dust or mold, or to food allergies. Your healthcare provider can discuss the most appropriate test if you have asthma.
How Is RAST Performed?
Then, the IgE levels in your blood sample are measured. These values are recorded in the RAST test list on your lab report.
What to Know About High Immunoglobulin (IgE) Levels
How Accurate Is the RAST Allergy Test?
As straightforward as a RAST test may seem, it has some definite limitations. While a RAST test can detect the concentration of IgE antibodies in your blood, it cannot predict how you will respond to the allergen associated with it.
Not everyone with the same concentration of antibodies will react in the same way, either.In some cases, a person with a relatively low concentration may have a severe reaction when exposed to an allergen.
Or, someone with a high concentration may react mildly or not at all. In this case, the person isn’t truly allergic even if the blood test is positive. People with low concentrations of allergen-specific antibodies tend to have a low chance of reacting to a possible allergen in daily life, especially if a skin prick test is also negative.
The Difference Between Blood Tests and Skin Tests for Allergies
Interpreting Your Results
Doing so can determine at which lgE level a person is more likely to experience an allergy to a specific allergen.
These values provide labs with the numeric references they need to interpret a blood test result. Each allergen has its own reference value which the lab will interpret individually.
What Is a Positive RAST Test?Most labs will report the RAST findings on a scale of 0 to 5 or more. A 0 value suggests a low likelihood of an allergy. Positive values mean there’s a likelihood of an allergy, which increases with a higher number. Some labs report the IgE values in micrograms per milliliter (μg/mL). An experiencedallergistwill know what this means.
What Is a Positive RAST Test?
Most labs will report the RAST findings on a scale of 0 to 5 or more. A 0 value suggests a low likelihood of an allergy. Positive values mean there’s a likelihood of an allergy, which increases with a higher number. Some labs report the IgE values in micrograms per milliliter (μg/mL). An experiencedallergistwill know what this means.
Disadvantages of RAST Test
A RAST test can be used to direct some aspects of allergy treatment. For example, they can sometimes help to determine whether a child is showing signs of outgrowing a food allergy.A RAST should never be used in isolation but rather to support the findings of other tests.
In the era of genetic medicine, other blood tests may be more accurate than the RAST in identifying immunoglobulin E (IgE) antibodies in a targeted way. Tests have become more sensitive and specific, leading to more personalized treatment options. These continue to evolve; for example, some tests have found food allergy-related IgE antibodies in human tears when they weren’t detectable in the blood sample.
Allergies and At-Home Tests
The Best At-Home Allergy Tests for Quick, Reliable Results
Summary
The RAST test is a blood test that can be used to check for allergies. Newer tests that have been developed, including the ELISA, have made the RAST test somewhat dated. It also can be less accurate than a skin test, though it may be a better option in specific circumstances, like allergies in children or people who take certain medications.
RAST tests may offer clues about your symptoms, but your allergist is likely to use them in combination with other allergy tests. If you have specific questions about your RAST test, your allergist or immunologist is the best person to ask.
Food Allergy Diagnosis and Treatment
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10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Asthma and Allergy Foundation of America.Allergy diagnosis.University of Michigan Health.Evaluation, testing and diagnosis for food allergies.Garriga-Baraut T, Moncín MMSM, Tena M, Labrador-Horrillo M; Comitè d’Al·lèrgia Respiratòria de Catalunya, Spain.INMUNOCAT study: The impact of molecular diagnosis on immunotherapy prescription in pollen polysensitized patients from Catalonia.Clin Transl Allergy. 2023;13(5):e12246. doi:10.1002/clt2.12246Ansotegui IJ, Melioli G, Canonica GW, Caraballo L, Villa E, Ebisawa M,et al.IgE allergy diagnostics and other relevant tests in allergy, a World Allergy Organization position paper.World Allergy Organ J. 2020 Feb 25;13(2):100080. doi:10.1016/j.waojou.2019.100080National Library of Medicine: MedlinePlus.Allergy blood test.American College of Allergy, Asthma, & Immunology.Testing & diagnosis.Muthupalaniappen L, Jamil A.Prick, patch or blood test? A simple guide to allergy testing.Malays Fam Physician. 2021;16(2):19-26. doi:10.51866/rv1141Centers for Disease Control and Prevention: National Center for Environmental Health.Allergy testing for persons with asthma.Bernstein IL, Li JT, Bernstein DI, et al.Allergy diagnostic testing: an updated practice parameter.Ann Allergy Asthma Immunol. 2008;100(3 Suppl 3):S1-S148. doi:10.1016/s1081-1206(10)60305-5National Institute of Allergy and Infectious Diseases.Guidelines for the diagnosis and management of food allergy in the United States.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Asthma and Allergy Foundation of America.Allergy diagnosis.
University of Michigan Health.Evaluation, testing and diagnosis for food allergies.
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National Library of Medicine: MedlinePlus.Allergy blood test.
American College of Allergy, Asthma, & Immunology.Testing & diagnosis.
Muthupalaniappen L, Jamil A.Prick, patch or blood test? A simple guide to allergy testing.Malays Fam Physician. 2021;16(2):19-26. doi:10.51866/rv1141
Centers for Disease Control and Prevention: National Center for Environmental Health.Allergy testing for persons with asthma.
Bernstein IL, Li JT, Bernstein DI, et al.Allergy diagnostic testing: an updated practice parameter.Ann Allergy Asthma Immunol. 2008;100(3 Suppl 3):S1-S148. doi:10.1016/s1081-1206(10)60305-5
National Institute of Allergy and Infectious Diseases.Guidelines for the diagnosis and management of food allergy in the United States.
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