Allergy Testing

Important definitions:

Allergen: Something to which the immune system develops an allergy; these are usually proteins in things such as pollens, dust mites, and some molds. Antibody: A specialized protein called immunoglobulin (Ig). There are many subtypes including those that are responsible for allergic reactions, IgE. Gold standard: For the purpose of our discussion: a diagnostic test which is considered to be the most reliable. When evaluating the usefulness or reliability of a new or different test, that test is compared to the “gold standard” test. Hyposensitization injections: Another name for allergy vaccine injections or allergy shots. These injections reduce the sensitivity of the patient to allergens. IgE: The allergic antibody; immunoglobulin type E.

Allergy testing is done to determine what allergens might be responsible for a pet’s allergy symptoms. Allergy testing does this by looking for the presence of allergic type antibody (IgE) specific for common allergens. Two areas of the body are commonly tested for the presence of specific IgE: the skin and also the blood.

Intradermal Allergy Testing (or skin allergy testing) is considered the gold standard of allergy testing. It is very similar to skin allergy testing that is performed in humans. In pets, it involves the injection of small amounts of allergens in an organized fashion in the skin. When a pet is producing IgE that is specific for the allergen injected during the test, the IgE produced by the pet causes the skin to become red and puffy exactly where the allergen was injected. A scoring system is used to differentiate positive injection sites from negatives. Training and experience are needed to evaluate the injections properly. Skin allergy testing, like blood allergy testing, is reliable only for non-food allergens such as pollens, dust mite, and molds.

The procedure for intradermal allergy testing is similar to what is done with people with a few changes. First, a light sedative is given to reduce the pet’s anxiety since they probably don’t understand that the testing is being done to help them. This also reduces the chance that the pet’s stress will affect the reliability of the results. Another difference compared with testing in humans: an area of hair, usually 6”x8” needs to be clipped on one side of the body, so that the location of each individual injection can be determined by using a marker. The results of the test are determined within15-25 minutes of the injections and the pet is given a medication to reverse the effects of the sedative. This is a straight forward procedure and our expertise makes it as easy as possible for your pet. Most pet show no drowsiness after the sedative is reversed.

Blood or serum allergy testing tests the blood for the presence of specific IgE. The best use for serological testing is when the results of skin testing do not correlate well with a pet’s history of symptoms. Another reason is if the pet cannot have skin testing performed because of medications the pet has recently received. One would think that the specific IgE found in the blood would be the same as what is found in the skin. However, that is rarely the case. Although there is usually some overlap between the two tests, the results are almost never identical. The reason may be due to production of specific IgE in the skin and not in the blood. Since useful information can be obtained both from the blood and from the skin, we normally recommend all pets starting on hyposensitization injections (allergy shots) have both tests performed. The choice of laboratory used for testing is important as different labs use different methods for the analysis and test for different allergens. In addition, the serum sample must be shipped so that it is not exposed to heat greater than 135 degrees Fahrenheit, which is the temperature that destroys IgE.

Once the results of the intradermal and blood tests are known, an experienced allergist can select which allergens should be incorporated into the allergy vaccine. It is not uncommon for results of tests to include allergens that are important for a pet as well as allergens that are less important or not important. Including unimportant allergens in an allergy vaccine takes up valuable space in the formulation, which could be better utilized for allergens that are important to the pet. Additionally some allergens share similarities and with other allergens and that should be taken into consideration. Some pets may have a tendency or a history of allergic reactions to other types of injections and that should be taken into consideration as well with the formulation. Dr. Byrne has years of experienced and years of specialized training to make the best possible formulation for your pet.

See also… Allergy Shots