A RAST test (radioallergosorbenttest) is a blood test used to check for allergies.
Many healthcare providers use skin tests to screen for theseimmunoglobulin E (IgE) antibodyresponses in your blood.
This article explains how the RAST test is performed, along with its limitations.
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It also discusses how to read a RAST test and what the values on your test may indicate.
What Is a RAST Test?
RAST stands for radioallergosorbent test.
RAST also can be used to monitor IgE levels in people who already have a food allergy diagnosis.
The ImmunoCAP test is a preferred method, allowing for molecular-level diagnosis in support of more targeted treatment options.
RAST Tests vs. For example, young children may be less likely to cooperate with a skin prick test.
The long-term use ofsteroidscan interfere with skin tests.
Keep in mind that not all tests are used for the same types of allergic reactions.
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.
What Can RAST Test For?
Your healthcare provider can discuss the most appropriate test if you have asthma.
How Is RAST Performed?
When your healthcare provider orders a RAST test, you will be asked to provide a blood sample.
The lab will then use the RAST technology to look for allergen-specific IgE antibodies.
This is done by adding specific allergens to the blood sample to see if IgE is produced in response.
Then, the IgE levels in your blood sample are measured.
These values are recorded in the RAST test list on your lab report.
How Accurate Is the RAST Allergy Test?
As straightforward as a RAST test may seem, it has some definite limitations.
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.
This can be determined by comparing IgE concentrations to a reactive allergic response in a food challenge.
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 (g/mL).
An experiencedallergistwill know what this means.
Disadvantages of RAST Test
A RAST test can be used to direct some aspects of allergy treatment.
Although predictive values have been established for some foods, those levels sometimes vary by age.
Moreover, researchers haven’t determined the predictive values for all foods.
Tests have become more sensitive and specific, leading to more personalized treatment options.
At-home kits to test DNA for allergies also exist but their accuracy is not confirmed by research.
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.
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