Everybody has made absolutely wonderful points, but we're kind of skirting away from the original poster's point: when should you go to the vet?
I look at it like this: your pet is essentially a small fuzzy child. If you don't want to foot expensive medical bills, because yes, vets are expensive (one of the reasons I'm in vet-med school right now
), then you probably shouldn't get a pet. Regardless, if it's a malady you would go to the doctor for (itchy sores, eye problems, limited mobility, whatever), then you should take the pet in. It might be an easy fix, but it's worth the bill if it means peace of mind. You can't really make a "defined" list, because there are just too many medical issues to cover. It really boils down to common sense. You know your pet, and you know their usual behavior (if it is a new pet, a puppy, or a kitten, any odd behavior should be immediately acknowledged just to be safe.) And as to calling the vet to ask, any good and caring vet, or vet tech, will answer your questions--I actually had to do this this week over my male kitties. I wanted to price vaccinations and castration surgeries to see who would give me the care I seeked for my pets as well as a reasonable price--I personally use 3 vets for my pets--one for emergency-only visits, one for regular check-ups, and one for surgeries. I have records on all my kitties, keep all three vets up to date, and they all know how I handle my kitties...I also have a LOT of experience with animals, so that does make a little difference as to why I operate in this way. The bottom line is this: if you are unsure as to what to do, then you should call your vet, discuss the issue, and go from there. Only your vet can give you the medical advice you need.