An overview of allergy testing and what is involved.
You suspect you have an allergy, but you’re not sure what it is exactly. Is it something you ate, touched or inhaled?
Consult your doctor. He may recommend that you go for allergy testing, which is used for analysing reactions to specific allergens. This can be helpful to confirm the diagnosis of allergic rhinitis and aid in its treatment. If specific allergic triggers are identified, then appropriate avoidance measures can be recommended.
The most commonly used methods of determining allergy to a particular substance are allergy skin testing and in vitro diagnostic tests, where blood samples are tested in the laboratory.
Skin testing can take the form of:
(a) Skin prick testing: This entails a scratch or a prick on the surface of the skin with small amounts of different allergens, in order to observe the immediate phase reaction, which may show as a wheal (swelling) and/or erythema (redness).
(b) Intradermal testing: This involves injecting the allergen into the skin’s dermal layer. This test allows the activation of the inflammatory cells of allergy, known as the mast cells. The intradermal testing might precipitate a stronger allergic reaction, and hence will require a specialist doctor to be present when it is done.
Blood testing can take the form of:
(a) Radioallergosorbent test (RAST): Done in the laboratory, the RAST checks the blood sample for specific IgE to find out what substances you may be allergic to. IgE, or immunoglobulin E, are a class of antibodies that our bodies produce in response to allergens. These antibodies lead to the release of allergic mediators (chemicals) which cause allergy symptoms like nasal congestion, nose itch, and more.
The test records the total serum IgE, which is the measurement of the total level of IgE antibodies in the blood. While patients with allergic rhinitis are more likely to have an elevated total IgE level than the normal population, this test is neither sensitive nor specific for allergic rhinitis.
(b) Enzyme-linked Immunoassays (ELISA / EIA): These blood tests are sometimes used to check for the presence of IgG antibody levels in patients with food allergies. IgG, or Immunoglobulin G, are another class of antibodies that the body produces, often to fight pathogens.
This is based on the findings that certain subclasses of IgG have been associated with the in vitro degranulation (immediate release of chemicals) of basophils and mast cells (both are allergic cells), the activation of the complement cascade (both of which are important mechanisms in allergy and anaphylaxis), and the observation of high circulating serum concentrations of some IgG subtypes have been measured in certain allergic individuals.
The premise behind this testing is that high levels of IgG antibodies are occasionally correlated with clinical food allergy signs and symptoms. With these tests, the physician may advise the patient to avoid certain foods.
Note: There are many arguments/controversies for and against the theory of IgG subclass antibodies being involved in allergy, which we will not go into here, but you may read this, this, and this if you’re curious.
Whichever allergy tests you take, it is important that the results are interpreted by a specialist who knows your symptoms and medical history, and can therefore advise you on your condition and treatment options. Allergy test results are not and should not be taken as diagnoses.
