How to know if your cat needs a vet
For the first time cat owners this may be one category they are not versed at. I was not either however you learn with time. One thing I would suggest is to have your cat checked out by a vet as soon as you bring it home. It is like a version of regular human check up which should help you establish if your cat is in good condition health wise but also if there are possibly some prior illnesses or diseases you were not aware about and what are the possible treatments. Sometimes time is of essence especially in case of emergencies or accidents.
What I have learned over time being a pet owner through my daily interaction with both my dog and over the last year and a half my cats, sometimes it is pretty obvious they are not feeling well. And I am not talking about waking up in the morning and finding a few puddles of vomit on the floor.
If you pet your cat and play with it on regular basis you will be able to deduct certain changes in behavior and habits that may be a signal for a more serious condition. So observation is the key.
While this may sound gross it is necessary - you will have to familiar yourself with your cat's urinary tract and bowel movements. This cannot be stressed enough. After a few days you will notice how frequently your cat urines and in what quantities. Also take note of the color, size, consistency and the smell of feces. This might be a bit too much to handle especially for the first time cat owners however any changes in your cat's urinary tract and bowel movements in most cases are a sign your cat should see a vet, whether it is diarrhea, inability to defacate or inability to urinate properly.
Your cat's eating habits can also be a signal your cat is not feeling in top condition. Even though cats can be a finicky bunch when it comes to food, loss of apetite can be a signal for a more serious condition. The same applies in case your normally playful and exhuberant cat becomes subdued all of a sudden.
Another thing that may happen is that your otherwise litter trained cat starts urinating in place other then the litter box. Unless there has been some changes in your households there is no reason why this should happen. It can be there are problems with the cats urinary tract and you should take it to the vet.
As stated before, observation is the key. While with one of my cats I have learned it is nothing to get worried about if he up-chucks from time to time (he does have a tendecy of wolfing down food and sometimes he is a bit too greedy for his own good) with my other cat I have learned if he vomits more then twice it is time to go to the vet. These are just some of the guidelines to follow, if you have any doubts visit a vet, it is always better to be safe then sorry.