I have a medical claim that is in appeal with my insurance company. The doctor's told me that I am still responsible for paying the bill while it is in appeal and they will just reimburse me later. Is this true?
Generally you are responsible for medical bills if your insurance company won't pay. You didn't mention how large this bill is, or whether you can afford to pay it. If you can afford to pay, I would recommend you do so before it ends up as a collection account on your credit report.
If you can't afford to pay it, see if the medical provider will allow you to make payments while you appeal it with the insurance company. That may also be a good strategy if the bill is very large and you will need to try to negotiate a discount with the medical provider.
If they do agree to allow you to make payments, try to get something in writing that will confirm your arrangement so it doesn't end up in collections and on your credit report.