Not to be confused with a medical peer review, this is solely something that happens when a request for services has been denied by the insurance company.
This can also be called a "doc to doc" appeal, this is typically a phone conversation between a physician at an insurance company (the one that's refusing to pay for services) and the patient's attending physician (the one whose requesting services).
Anyone on the patient's team (social worker, case manager, why, even, believe it or not, the patient himself!) can initiate this with the insurance company when a request has been denied, but it's infinitely better to make sure your doctor handles the conversation.
Often times, getting the two doctors on the phone can make a world of difference to the initial denial. One of our patients had been routinely denied acute rehab after his open heart surgery which was not at all routine. When the patient's cardiologist got on the phone with the insurance doctor reviewing the case, she shared critical clinical and surgical information that the insurance doctor was not aware of. Once she heard the unusual circumstances, she immediately approved the rehab.