The next main reason is a non covered procedure. This is a very common reason for return of claims too. All insurance companys have different coverage dependent on the policy that the patient has. Most policies cover things such as well check exams,sick visits and common things like this but when it comes to more specific visits, each policy can differ on what is covered or not. So a lot of practices may get prior approval for a procedure before doing the procedure. This helps to keep the lose of money down in a practice and insures them that they will be payed for the procedure.
Another reason that a claim maybe returned is that the patient may have a deductible that has not been met yet for the year. Even if the patient pays their copay at the time of the visit, if they have a $500.00 deductible yearly and have only met $250.00 of it, then the insurance company will deny the claim. This intern having the claim returned to the practice for them to bill the patient for.
So as you can see there are alot of reason a claim could be returned from an insurance company. This is just a few reason that they could be