I know that you can not rely on blood tests. And I am going to tell you an example with my dogs.
My dogs were looking normal until 1 had a seizure after 13 years of never having one, and continued to have small tremors. The another dog who had very few seizures was now having them more frequently (now at once a week) and they were clustered grand mal's.
Well, their blood tests shows nothing too out of wack and nothing obvious. I chose to go to a Homeopathic (eastern trained) Vet. She checked their tongue, their pulse and a few other things and was sure that their liver is having troubles with toxins. With treatments of herbs, ION Cleanses, and accupunctures they are doing well - Seizures have diminished back to normal.
By the time it shows up in blood work - damage has happened and in some cases it could be permanent.
Thanks to these healthy alternatives we can help our body stay healthy and hopefully we won't need to take medications to keep us that way.