Leah
I will never do annual bloodwork again. My cat Sasha had annual bloodwork. He also had an enlarged thyroid gland on a physical exam. Over the course of 12 months, Sasha had 5 SMDA tests and 3 renal panels. I was told that he went from stage 2 to 3 kidney disease over that 12 month period in spite of medication.
Here is where it gets interesting. Sasha was not symptomatic for kidney disease. He was symptomatic for hyperthyrodism. The vets put him on Calcitriol. That did nothing. Then he was on Semintra. That did nothing. Of course it didn't. He did NOT have protienura. He did NOT have kidney disease.
In my experience, vets are quick to upsell all things kidney. It's a money maker for them. I have also learned that bloodwork is useless if the vet does not have any diagnostic skills. Too many of them are trained to memorize a number. And that is more dangerous than not having bloodwork done. Because misdiagnosis happens.
In Sasha's case, his hyperthyrodism was affecting his kidneys. And knowing what I know now, his kidneys would have been just fine had the root of the cause, hyperthyroidism been treated.