How Canine Skin Allergy Tests Work
The purpose of a skin allergy test (also called an intradermal skin test) is to achieve an allergic reaction under your dog's skin with a minute amount of known allergens. To conduct this test, you may be referred to a veterinary dermatologist, who will sedate your dog and shave the hair off one side of his abdomen. The dermatologist will then use a special instrument to inject small amounts of known allergens in a prescribed order under the dog's bare skin. After a set time period (usually between 24 and 48 hours), the skin will be evaluated for any symptoms of allergic reaction, such as redness or swelling.
A positive reaction to an allergen results in your dog's skin swelling or becoming red and irritated, while a negative reaction shows no signs at all. The order in which the allergens are administered helps the dermatologist determine which ones are problematic for your dog.
Certain prerequisites need to occur in order for this test to be effective. It needs to be administered at a point in the year when your dog's allergies are not causing numerous symptoms. Your dog will need to be off other medications, such as steroids or antihistamines, for a period of time before the test is administered in order for it to be effective.
What Canine Skin Allergy Tests Can Diagnose
Intradermal skin testing is particularly effective at diagnosing atopic allergies in dogs. These allergies, which are the second most common canine allergy, show symptoms on the dog's skin after he inhales an allergen. About 75 percent of atopic allergies in dogs are effectively diagnosed via skin tests.
Allergens that can be identified by skin testing include dust mites, house dust, mold and pollen. These allergies can often be successfully treated with a series of what's commonly called allergy shots (or hyposensitization). Small amounts of allergen are administered to the dog to give his immune system the chance to build an immunity to the offending allergen. In time, the dog's body no longer views the allergen as a threat, and his symptoms disappear.
Food Trials
Since intradermal skin tests are not effective at diagnosing a canine food allergy, veterinarians have to find another way to test for food allergies, such as an exclusion diet trial. This special diet, which gives your dog the opportunity to eat new sources of protein and carbohydrate for a set time period, lets your vet evaluate the severity of your dog's allergy symptoms over a 12-week period.
If the symptoms subside, your veterinarian will test the food trial by reintroducing ingredients from your dog's former diet to try to create an allergic reaction. By this process of elimination, the cause of your dog's food allergy can be determined and a new diet plan can be created.