My practice performs blood tests before every surgery, even routine ones like spays, neuters, and dental cleanings. Our surgery packages include these tests in the pricing, and it's not an option that our clients can decline. Why? Because we feel it's important to the safety of the pet and many clients would decline because of perceived lack of funds. Just because a pet looks healthy externally doesn't mean that they really are healthy. Here's a case in point.
Today we had a puppy come in for a routine neuter. We had seen him for his vaccines and hadn't found any problems on routine exams and the owners hadn't reported any serious concerns that couldn't be attributed to normal puppy behaviors. As normal, we performed blood tests and were quite surprised at the results. According to the lab results this 19 week old puppy was in complete renal failure. All of his kidney values (creatinine, phosphorous, and blood urea nitrogen) were significantly elevated by several times and his red blood cell count was noticeably lower than normal. Why is the blood cell count significant? The kidneys produce erythropoetin, which is the hormone that stimulates the bone marrow to create red blood cells. If the kidneys are sufficiently damaged for long enough the hormone levels decrease and fewer red cells are generated. This normally happens in chronic kidney disease rather than acute, which means that this puppy had underlying problems for much longer than we had thought.
All of this sounds pretty bad and it normally is. Usually patients with values like this are very obviously sick, even critically so. Yet this puppy was doing pretty well. Or so we thought. No, he wasn't at death's doorstep, but there were some subtle signs that further questioning of the owner revealed. He had seemed to be drinking a lot of water, but that's not uncommon with puppies. He seemed "quiet" to the owners, but some puppies can be that way. He had vomited a few times, but not predictably or routinely, also something that puppies may do. Individually and even collectively these weren't outrageous symptoms. However, when combined with the laboratory tests they were early signs of an underlying problem.
Despite the fact that he didn't seem particularly ill, the pattern in the tests and the subtle symptoms could not be ignored. At his age, the most likely possibility was a congenital defect in the kidneys, though a previous toxin could not be ruled out. Whatever the underlying cause, once the kidneys are damaged they won't regenerate, so there wasn't much we could do for the puppy. The owners took him home and are looking into their options but will likely end up euthanizing him.
Preanesthetic blood testing really and truly is important!