Pet Health Information

Intradermal Skin Testing for Allergic Dogs and Cats

Skin allergies (also known as atopy and allergic inhalant dermatitis) are fairly common problem for some dogs and cats. Atopy has a genetic basis and causes an animal to be sensitive to substances in the environment, such as pollen, dust, molds, and grasses. Most animals are sensitive to more than one substance or allergen.

Allergic animals are typically extremely itchy. Often as a result of scratching, they also develop skin infections. Many animals will have trouble only at certain times of the year or certain seasons. However some pets will experience problems year round.

Once other possible causes of itchiness and skin infections are ruled out, we may recommend Intradermal Skin Testing (IDST) for your pet. The procedure is done by our dermatologist and takes about 40 minutes to perform. Most animals are sedated lightly with an injection. The fur is clipped from a rectangular area on the animal’s chest. A felt-tipped marker is used to make a grid of dots on the skin to mark the injection sites. We use 70 allergens in our IDST, so there are 70 dots. With a very small needle, a tiny amount of allergen is injected into the upper layer of the skin. A different needle and syringe is used for each allergen. The first dot is always histamine, which is the positive control and will cause the biggest reaction. The second dot is saline which is the negative control and will cause no reaction. After 15 minutes, each site is compared to the positive and negative controls and ranked on a scale of 1 to 4. A second reading is performed after 30 minutes.

While the animal is waking up, we evaluate the results of the test. Generally, a reaction of two or higher is considered significant and that allergen will be included in the allergy vaccine, we make for the animal.

The idea behind allergy vaccines is that once you identify what the animal is sensitive to, you can try to desensitize the animal. In the beginning, the vaccine is weak. Over the next subsequent weeks, the animal is exposed too increasingly greater amounts with each injection. The goal is to reach a point where the animal is desensitized and requires an allergy shot only about once a month to remain comfortable. Generally the process takes between 6-9 months for the pet to become desensitized.