RAST Testing

A RAST test is a type of blood test that allergists can use to test for suspected allergens. RAST stands for radioallergosorbent.  It is a type of blood test that can be used to diagnose certain types of allergies. It works by looking for an antibody in your blood called IgE.  When you have an allergy to something, your immune system will make more IgE that is specific for fighting that allergen.  RAST testing can tell you what your body is responding to with increased levels of IgE.

What are the Benefits of RAST Testing?

One of the benefits of blood tests such as RAST testing is that they are very standardized, meaning that the methods that are used in the laboratory vary little from location to location.  The RAST test is also a very sensitive test.  This means that if you have an allergy, there is a very high likelihood that RAST testing will find and confirm the diagnosis.  IgE antibodies are specific for each different allergen, so it can be a great way to investigate and diagnose very specific allergy responses.

RAST testing can also be helpful when skin-prick testing (an alternative form of allergy testing) isn’t possible, as in the case of someone who has very severe eczema or other skin disease.  Patients are often instructed to stop their allergy medicine in order for the test to show results.  However, with blood testing, you may not have to stop your medicine at all.  RAST tests are also useful if there are concerns about potential anaphylaxis or other severe reaction with exposure to a particular allergen.  RAST blood testing involves a single needle stick which may makes it an easier test to administer for younger children who may not tolerate the multiple needle pricks of skin-prick testing.

The drawbacks to RAST testing are that it can be more expensive and it takes more time for the results to come back, meaning you have to wait longer to get your diagnosis.