White Blood Cells in Dogs and Cats. The white blood cell count is a diagnostic tool for evaluating your pet’s health. When your veterinarian runs a blood test to determine what’s ailing Fluffy, do you ever wonder what exactly all those numbers mean? A simple blood test provides a lot of information about your pet’s health status. Among other things, the blood test quantifies the white blood cells in dogs and cats, and this information can contribute to an accurate diagnosis of the patient.