Skin tests for allergies are the most common methodology for detecting the kind and severity of allergies, however sometimes these are not possible or advisable. In such cases an allergy blood test is carried out to try and detect what a person is allergic to and to what extent.
When an allergy blood test may be advisable
If a person has a certain skin condition, it can prevent them from undergoing the usual prick test, patch or intradermal allergy tests. Also if they are taking certain medications, skin tests may not be possible and so blood tests to detect allergies may be required.
Different types of blood tests for allergies
The total IgE level test is designed to detect the allergen-specific IgE antibodies present in the blood stream.
The total levels of the IgE antibodies in the blood serum are measured. Blood tests such as the enzyme-linked immunosorbent assay (ELISA) or the radio allergosorbent tests (RAST) are usually used to detect allergies.
This kind of allergy test measures certain antibodies present in the blood samples, however it is now thought to be rather outdated.
The ELISA test
The enzyme-linked immunosorbent assay test is a more recent and technologically advanced type ofallergy blood test. It yields results by binding the antibodies present in the blood to the allergens. A developer is then added to the sample which changes color and this change in color is what will reveal the extent or type of allergy.
How blood tests for allergies are useful
The allergy blood test requires a small blood sample to be taken from the person and then analyzed to detect and identify specific antibodies. These tests are useful in recognizing exactly what reaction the body has to an allergen and whether it is a true allergy that the person has or a mere intolerance.
This type of allergy testing that uses blood samples also helps to determine the exact nature and extent of allergic activity in the person. What it may also be useful for is detecting whether a person has possibly ceased to be allergic to a given substance (out-grown allergies). For this reason such blood tests for identifying allergies have become more popular than in the past.
Limitations of allergy blood tests
Though blood sample allergy tests have become more accurate and technologically sound than in the past, there are still some limitations that they have.
- Blood tests are typically more expensive than the usual skin tests that more routinely used for detecting allergies.
- Blood tests are also less accurate in detecting allergies.
- There is the apprehension that blood tests could yield false positive results (indicate an allergywhen there is none present).
- Blood tests are also typically more expensive and also more time consuming (results will take a couple of days or longer) than skin tests.
It is best that the decision of whether to opt for allergy blood tests or any other kind of testing procedure be taken after considering all factors and in consultation with a trained and experienced allergist.