Allergy Testing 101: Which is More Accurate?
If you have an allergy, there are two types of tests that the doctor can perform to determine its cause and cure. First is by blood testing or RAST (Radioallergosorbent test) and by skin testing or skin prick test. In most cases, both can be performed depending on what type of allergy you have or either of the two.
RAST is a test that uses radioactivity. The lab technician will draw your blood then will add an allergen to the sample. It has a connection to immunoglobulin E (IgE) in your blood which is responsible for the allergic reactions in our body. He will then wash the blood and add a radioactive serum, which will enable the concentration of allergen-specific IgE in your blood. Lastly, the technician will measure the concentration of allergen-specific IgE in the blood sample. The higher the concentration, the higher the chances of that substance to have an allergic reaction to your body.
SKIN PRICK TEST
The skin prick test is a test that involves lightly pricking the skin on the back for children and on the forearm for adults with a needle or lancet. You will feel discomfort but won’t necessarily bleed. After that, the nurse will draw marks and will add a small amount of suspected allergen over the pricked area. Usually, he will scratch two additional substances such as histamine and glycerin or saline into the skin’s surface to have a more accurate test. An indication of an allergic reaction is if the skin developed a red, itchy bump 15-20 mins after the test has been done.
UNDERSTANDING RAST AND SKIN TEST
Most doctors today prefer not to use RAST as there are newer blood tests that emerged. Another option is an enzyme-linked immunosorbent assay, or ELISA test. Some believed that RAST is not that accurate because of its low sensitivity. Blood test is suitable for a person with severe eczema as skin test would be a risk.
Skin test is for airborne type of allergies and is also less expensive than RAST. It is not always accurate and sometimes indicates false positive and false negative results. You may react differently to the same test performed on different days and may react positively but not react to it in everyday life.
Due to mixed reactions, the doctor may perform RAST followed by a skin prick test or perform several blood tests and skin tests accordingly. He may also ask you about your medical history to provide more exact diagnosis and to help him decide what allergy test might be suitable for you.