When working up a dog with allergies, I perform several tests to rule out other diseases before launching into a food trial, intradermal test or serum allergy test. In my experience, dogs with allergies often suffer with skin infections caused by bacteria and yeast. Mange is a third common problem that can be misdiagnosed as allergies. Here’s a list of the tests I use:
1) Skin Scrape – Mange or infections caused by mites can look a lot like allergies. The dogs are really uncomfortable and the constant scratching causes skin damage. To check for mites, I scrape the patient’s skin with a sterile scalpel blade and examine the contents under a microscope.
2) Skin Cytology – Dogs with allergic dermatitis often suffer with secondary yeast and/or bacterial infections. In this test, a sample is collected, transfered to a microscope slide and examined for abnormalities. Samples are collected in a variety of ways including dry skin scrapes with a scalpel blade, pressing the slide directly onto the skin or using cellophane tape. Cotton swabs work well for ears.
3) Bacterial and Fungal Cultures – The skin is cultured to see what kind of organisms might be growing on it. Again, this is to test for secondary yeast and/or bacterial infections.
4) Flea Combing – Flea bites cause horrible itching in dogs. A special fine-toothed flea comb is used to find fleas on the dog. It is a good way to make sure the flea control is effective.
5) Skin Biopsy – Full-thickness biopsies of the skin are sometimes needed to differentiate allergic dermatitis from other skin conditions.
6) Blood Tests – Used to detect hormonal abnormalities that may cause skin problems.
As a veterinarian, I have to confess that dermatologic conditions can be vexing for everyone involved. The animals suffer greatly, vets and owners can too as they struggle to uncover the true cause of the problem. So, if you find yourself dealing with allergies or skin – hang in there! The answers can be hard to find but the relief to the animal is rewarding.