The RAST [radioallergosorbent test] blood test is used to determine if an individual has allergies that need to be addressed. It is different from a skin allergy test in that it measures specific antibodies that are developed by the body when an allergy occurs. It can help to track chronic or acute allergic symptoms as they occur and help individuals begin to identify their triggers.
The RAST blood test may also be ordered when someone may be exposing themselves to low levels of an allergen to desensitize themselves from the allergy. The one limitation of this test is that because it measures IgE that can be present for years after an allergic reaction, it can only provide general information about an allergy.
When Should I See a Doctor About the RAST Blood Test?
A medical provider will typically order the RAST blood test whenever there are signs and symptoms of an allergic reaction present. This includes hives, eczema, eyes that are red and itchy, dermatitis, chronic coughing, asthma, and itching within the mouth. Some allergic reactions may also cause abdominal pain, frequent vomiting, or frequent diarrhea.
Severe allergic reactions that include swelling within the face, neck, or throat should be evaluated immediately because this condition is considered a medical emergency. The RAST blood test may be ordered after symptoms are brought under control to determine what may have caused such a severe reaction.
What Do My Test Results Mean?
After the blood draw occurs, the testing laboratory will bind the suspected allergen with the serum that was collected. If there are antibodies in the blood for that allergen, then they will bin themselves to it within the serum. Based on the amount of reaction that occurs, medical providers can determine how severe an allergic reaction to specific substances happens to be.
The RAST blood test uses a scale that is scored from 0 to 6. A 0 score indicates that IgE that is allergen specific is either absent or it is undetectable. A score of 6 indicates that there is an extremely high level of allergen specific IgE present and that care should be taken around that substance to avoid a potentially life threatening figure.
Scores that are in the 1-2 range may indicate low level antibodies from a trigger that may not create a serious reaction, but could one day grow into something more severe. Scores in the 3-5 range will typically cause a medical provider to recommend avoiding those triggers as often as possible. An EpiPen treatment may be recommended or prescribed for carry if any test is positive.
Will Other Tests Be Performed?
It is very common for a medical provider to order a series of allergen tests in order to identify all of a person’s triggers. This may include skin pricking or scratching test, patch testing, or oral food challenges. The goal is typically to eliminate items one by one to determine what is causing the allergy. Although some people may choose to do some testing on their own at home, all allergen testing should be completed under the care and supervision of a medical provider.
The RAST blood test is also known to provide false negative results from time to time. It is possible than an allergy exists, especially if the symptoms of one are being experienced. Certain individuals who have an autoimmune issue, such as those with Celiac disease, may also test positive on the RAST if they have been exposed to gluten or their specific trigger in the recent past.
Even mild allergies should be evaluated by the RAST blood test or other testing recommended by a medical provider. Reactions can be quite variable in nature and sometimes mild reactions can quickly turn into severe ones that may even include the whole body.
Children sometimes have the ability to outgrow some of their allergies, but most adults will experience reactions to triggers throughout most of their lives. Mild allergies can sometimes be controlled with proactive and reactive medication, but the best solution is to avoid all triggers as much as possible.
The RAST blood test results explained here will give you the information needed to let you know about your triggers so they can be avoided. Develop a treatment plan with your medical provider in case an unintended exposure does occur so that your health does not necessarily need to be threatened because of a severe allergic reaction you knew nothing about.