Thank you for your recent inquiry.
RAST testing is a term that is commonly used to describe what is really an ELISA test to specific IgE antibody to allergens. It is a valid test and detects when a person is sensitized to an allergen. It has the same significance therefore as an allergy skin test. However, the demonstration of sensitization does not always correlate with symptoms. One can be sensitized to a food or an inhalant and not have any problem when they come in contact with either. So, the interpretation of a "RAST" test requires clinical decision making and a carefully performed medical history.
You are correct in that this test can be performed for both foods and inhalant allergens including pollen, dust mite, mold spores, and animal dander.
The cost and turnaround time for results varies from lab to lab. You would need to check with the lab utilized to obtain that information.
RAST tests may be used to guide avoidance procedures and environmental control measures. For example, if the history is consistent with symptoms induced by exposure to cats, and a RAST test is positive for cat, consideration should be given to instituting environmental control or avoidance measures.
In the hands of properly trained allergists/immunologists, RAST tests can be used to determine which allergens should be contained in an extract used for allergen immunotherapy. In these instances, they serve the same purpose as an allergy skin test. In general, they are usually more expensive than skin tests, and perhaps slightly less sensitive in most instances.
Thank you again for your inquiry and we hope this response is helpful to you.
Phil Lieberman, M.D.