Atopy in cats is the result of an allergic overreaction by a cat’s immune system to something that it comes into contact with in the environment, which is called an “allergen.” Usually, the cat interacts with the allergen through physical contact or inhalation. The most consistent signs of feline atopy are skin inflammation and intense itchiness (pruritis), which can lead to weeping sores, scabs and other self-trauma, as well as some dramatic behavioral changes. Unlike dogs, atopic cats often also develop breathing difficulties, symmetric hair loss and other skin (cutaneous) lesions, in addition to pruritis. A veterinarian presented with a cat showing this constellation of symptoms will take a thorough history from its owner and conduct a comprehensive physical examination. This will include a detailed dermatological check-up for the presence of any obvious external parasites such as fleas, lice, mites or ticks. The veterinarian may also take deep skin scrapings and samples of plucked hair to look for further evidence of parasites. Samples taken from the cat’s ears and from any oozing skin sores can be sent to a laboratory for microscopic examination, which can be quite helpful to determining the cause of the cat’s discomfort. In a nutshell, to diagnose atopy, the veterinarian needs to systematically rule out all other possible causes of the cat’s condition.
Based on the results of the initial evaluation, the veterinarian will probably recommend taking blood and urine samples for routine assessment. The results of these tests will typically be fairly normal in cats whose symptoms are caused by immune-mediated atopy rather than by something else. Advanced skin allergy testing is available for cats and is conducted by referral to a veterinary dermatological specialist. Animals that are taking oral, injectable or topical steroid medications should be weaned off of those treatments for 1 to 3 months before skin allergy tests are performed, because they can skew the test results and affect their reliability. Other drugs and supplements can also interfere with the results of skin tests. Intradermal testing is the gold standard for atopy in cats. It does require sedation and substantial clipping of the kitty’s fur. Blood (serologic) tests are also available but are much less reliable. Probably the best way to diagnose atopy in cats is to conduct both skin and serologic tests, but this certainly will increase the diagnostic expenses.