sick cat?

Question
Hi, I have a mix breed cat and he's probably about 10 years old. He typically eats A LOT, and he wasn't fat, but not very trimmed either. Lately he hasn't been finishing his food, he drinks water non-stop and he's gotten skinny and I can feel his spine when I pet him. Also he's shedding a lot(his ears are almost bald), and I have had to change his litter box very frequently. I know he's old, but I'm wondering if there's something else wrong? I had thought maybe it was something with his kidney's, but really I have no idea. This has all happened over a matter of two weeks or so. I was wondering if these are signs that he's sick (and if you know what the problem might be), or he's just old.
Thanks!
Ellen

Answer
Hi Ellen.  I think you may be on to something about his kidneys.  He is about the age when kidney failure becomes a real concern, and the signs are dead on.  It frequently sneaks up on us out of the blue.  But there are other possibilities, such as a bad infection or a B-12 deficiency.  I think you should certainly get him to the vet for an exam and some blood tests.  These aren't normal signs of aging and are definite signs of illness.  Hopefully it will be something easily treatable.  

Most vets will not think to test for his B-12 level, unfortunately, and you may need to request it if all his other tests come back normal.  They still may be reluctant, and even though my vets have thought it would be a waste of money, three of my cats have had undetectable levels.  Regular B-12 injections given at home have brought them back up to a normal weight.

I hope it turns out well!

Jessica