Allergy Testing: Blood Tests


When faced with a potential food allergy diagnosis, allergists use two types of tests to determine whether a patient is allergic. While history of reaction to an allergen is the only surefire way to determine a true allergy, skin prick and blood tests are also used. This article will discuss blood testing.

There are a few different types of blood tests available. The test used primarily depends upon your allergist. The RAST test (short for radioallergosorbent test) is a common one. Testing involves a blood draw and samples sent to a lab.

The RAST test detects the amount of IGE that reacts specifically with suspected or known allergens. IGE, or Immunoglobulin E, is the antibody to the allergen in question. If test results show a high level of IGE or antibodies to peanut protein, it is suspected that the person has a peanut allergy.

As with skin prick tests, there are false positive results with RAST tests as well. Eczeam seems to play a role in that it can cause high total IGE levels. While rare, some individuals with extreme eczema will show antibodies to various allergens and not be allergic.

The best way to determine a true allergy is to weigh skin prick and blood testing results along with history of reaction. If there is no history of reaction and/or the allergen can not be identified, it is sometimes best to do both a skin pick and blood test. However, it is not advised to test for foods that are not suspected--due to the high rate of false positive results.

If you have questions about allergy testing or your own testing results, you should discuss them with your allergist.