A diagnosis of a particular food allergy can be challenging, but there are methods to determine what is causing the symptoms in your cat. A food allergy test can be performed, either with a blood test or a skin test. The blood test can measure the IgE antibody count and type that is present in the bloodstream, while the skin test injects various allergens into the skin to see which one causes a reaction. These allergy tests are not completely accurate, and they are often performed when other methods have failed to produce a diagnosis.
The main diagnostic method for a possible food allergy is to change your cat’s diet. There are many types of diets available, but your veterinarian will recommend one that contains ingredients not already in your cat’s current diet. This can be a protein change, such as changing from chicken or fish to rabbit or duck. It could also be a grain, corn, or soy free diet, a homemade or raw diet, or even a hydrolyzed diet, which breaks down the proteins into smaller pieces that are unrecognizable by the immune system.
The specialized diet needs to be fed for 4 to 12 weeks, without any treats or other foods given that are not made with the same ingredients. Often, to confirm the findings from the results of this diet change, the old food may be reintroduced afterwards to see if the same reaction occurs. This method can help to make a diagnosis of a grain allergy.
In some cases, your veterinarian may take skin or intestinal biopsies for further testing to confirm that an allergy is the problem, although it cannot help to determine what your cat is allergic to.