This falls under Utilization Review. There are guidelines for every diagnosis and procedure that have the expected number of days IP for that particular thing. The approval is set at that amount. These guidelines are not just set by the insurance company, but there are standard Length of Stay (LOS) tables from medical professionals.
Utilization Review includes Concurrent review...this is where the insurance companies RN case manager calls the hospital and/or doc and they discuss an update of your status, complications, additional procedures, and other issues that may extend your stay. This is done while you are in the hospital. I actually have been released in less than the projected days in the past and the RN called after I was already released----that was a shock to me.
Yes, I work for an insurance company, but I will neither villify nor defend them as they all are different.
PS...you can always call your insurance company to talk to a Nurse Case Manager. You can give them more information on your particular situation. Just know that they will call and check on you too. This can be a good thing for those that don't have a doctor who is guiding them through their choices especially if you have a good case manager. Sometimes I have found them just intrusive and I am pretty self sufficient. It all depends on your needs.