A thorough exam will be done on your pet the morning of anesthesia, but many conditions cannot be diagnosed with the examination. We recommend appropriate blood tests to screen for internal problems that we cannot detect on the physical exam. Your pet can’t tell us what might be wrong, so our doctors will use your pet’s blood work to get a clear picture of what is going on beneath the surface. These tests identify pre-existing conditions thus improving anesthetic safety, and also provide valuable baseline data for future comparison.
There is an excellent video from the American Veterinary Medical Association on the importance of blood test for wellness exams, sick pets and pre-anesthetic testing.
Link to AVMA video