Never pay a bill from a medical provider (doctor, hospital, lab, etc..) until you've received your EOB (Explanation Of Benefits) from the insurance company. The EOB will outline what the doctor billed, the approved amount for the service, and how much of the bill you'll be responsible for. And, once you examine the EOB make sure it's correct. Then make sure what the insurance company says you'll owe matches the bill from the provider. If they don't match find out why.
I just received a bill for an x-ray I had at an urgent care facility when I broke my wrist back in March. The bill was only $24 so it wasn't something that I'd normally scrutinize, but I did just because I couldn't understand why I was responsible for the entire $24. After closer examination of the EOB I noticed that the provider was an out-of-network provider so they applied that amount to the separate out-of-network deductible (out-of network or non-participating providers are usually covered at a much lower rate and sometimes have a separate deductible as was the case for my insurance). HOWEVER, my arm was broken, so didn't that fall under the category of "emergency?" It's not like I could take the time flipping through a provider directory in the middle of a rural area trying to find an in-network provider. Yesterday I called the insurance company and told them it was an emergency and that they should treat the bill as if it were an in-network provider. The insurance company is reprocessing the claim and covering 90% of the bill. Instead of $24 I'll owe only $2.40. Granted my example doesn't contain large, shockingly high amounts, but the message is still clear -- always check your EOB and ask your insurance broker for help if you need to. They're on your side and not the insurance company's.