While blood testing isn’t the most widely used form of allergy testing, it is often used and is known as radioallergosorbent testing or RAST for short. This test is used in order to see what the blood level of an antibody (immunoglubulin E, or IgE for short) is in a patient’s body. This is a chemical that the body produces as a response to certain types of allergens. The body’s IgE level is usually higher whenever a patient has allergies or in asthma patients. RAST is most often used for those who are taking certain types of medications, including some antidepressants or antihistamines. These types of medications alter the results of the skin prick test in such a way that they become less accurate. Another reason why blood tests are sometimes used is because a person may have extremely sensitive skin, or a skin condition such as eczema. In such cases, the progressive testing would only irritate their skin more, causing them a great deal of discomfort.
For this type of allergy testing, a person must have their blood drawn in the normal fashion. Before having this blood drawn, the patient should not drink alcohol or beverages containing caffeine. With this in mind, you should know that only a small tube of blood is required for this testing to be done. The blood sample is then placed upon a piece of paper that has been specially treated. This paper is then sent to the lab where they will determine whether antibodies to any of the allergens that are being tested are actually present. If these specific antibodies are detected, then a person may have an allergy to that certain thing. Usually a lab will let you know the results of your blood test in about seven days. There are two different types of results that can be had whenever this testing is used.
The first result that some people may get is that their test is returned to them as being “normal.” This means that the test was negative. In technical terms, this means that the amount of immunoglobulin E (IgE) in a person who does not have any allergies is the same as they are in this patient.
The second result that some people may get is that their test is returned to them as being “abnormal.” This means that their test was positive. In this case, the levels of immunoglobulin E (IgE) antibodies for a specific allergen, or group of allergens, are four times that which is considered to be normal.
It is important to understand that allergy blood tests are not nearly as sensitive as skin tests are. For this reason, some people who have a positive reaction to a skin test can then take a blood test and receive a negative reaction. This is why doctors prefer to do the skin test and not the blood test. However, the blood test is a nice test to use if you are in need of a second resort due to the aforementioned problems keeping you from being able to get a skin test.