Canine Hot Spots - Allergy Testing
(Continued article ... page 5 of 6)
| Definition / Causes | Parasitic Allergens | Allergy Testing |
| Environmental Allergens | Other Causes | Prevention |
Principles of Allergy Testing
In general, mixed allergen testing (combining antigens from different sources together, in the same way a human might be tested, say on his or her back) may be performed. Since the purpose of testing is to identify a specific allergen or allergens for immunotherapy, testing each allergen individually is the preferred method.
Common Pet Allergens
Common testing allergens include: grasses, trees, shrubs, weeds, molds, house dust mite bodies, mite eggs, mite larvae, mite feces, fleas, ants, flies, cockroaches, mosquitoes, moths, feathers, nylon, wool, silk, and tobacco. Food allergen testing is rarely effective for identifying food-related allergens; therefore, food elimination testing is the preferred method for screening for food allergies.
Selection of allergens for the purpose of treating dogs with immunotherapy (hypo sensitization treatment) may be done either through intradermal testing or in vitro testing. Each method has its strengths and weaknesses in terms of laboratory analysis.
Intradermal Testing
With intradermal testing, a commercially available antigen is selected and injected under the skin and the site of the injection is observed for signs and intensity of an allergic response. Many dermatologists utilize intradermal testing because it has a high level of specificity and thus positive results are more likely to be true-positives. The main limitation with this test is the occurrence of false-negatives because of poor sensitivity associated with this form of allergen testing.
In Vitro Allergen Testing
An alternative to intradermal testing is in vitro allergen testing. This second method requires reacting serum from the dog with a commercially-available antigen that has been bound to a solid substrate in a radioallergosorbent test (RAST) or enzyme-linked immunosorbent assay (ELISA), which measures the amount of IgE in the patient's serum that binds to the allergen. This test is particularly useful in evaluating dogs that have already undergone or are continuing treatment with glucocorticoids (since these drugs will inhibit intradermal test reactions yielding false-negative results). However, in vitro allergen testing has a higher degree of non-specificity and, therefore, false-positive results. Recent modifications to methods of in vitro allergen testing by the Veterinary Allergy Reference Laboratory (VARL) have provided a means to increase the level of specificity of these in vitro tests aimed at detection of IgE through the use of monoclonal anti-IgE reagents. Additionally, this testing method also seems to provide comparable specificity while providing greater accuracy compared to intradermal testing for detecting insect-associated allergies.
continued »»
