One in five operations may lead to surprise bills, even when surgeon and hospital are in-network

On average, that potential surprise bill added up to $2,011, a team from the University of Michigan reports in the new issue of JAMA. That's on top of the nearly $1,800 the average privately insured patient would already owe after their insurance company paid for most of the costs of their operation.

All the patients in the study chose a surgeon who accepts their insurance, and had one of seven common, non-emergency operations at an in-network hospital or at an outpatient surgery center.

But they still ended up potentially owing large sums to pay other people involved in their operation or their follow-up care. The average potential surprise bill ranged from $86 for medical imaging specialists involved in a hysterectomy, to more than $8,000 for surgical assistants involved in a breast lumpectomy. These out-of-network bills were significantly more common for patients who had complications after surgery.

If the patient had an outpatient procedure with an in-network surgeon, but it took place at an ambulatory surgery center that was out-of-network, the potential surprise bill could add up to more than $19,000.

"These are eye-popping numbers, which most clinicians are likely unaware of, and which patients can't prepare for," says Karan Chhabra, M.D., M.Sc., the study's first author and a National Clinician Scholar at the U-M Institute for Healthcare Policy and Innovation, which funded the study.

The study looked at the claims that a large insurance company received from in-network and out-of-network medical providers for more than 347,000 patients under age 65 who had one of the seven operations between 2012 and 2017. Even though all the lead surgeons and the surgery locations were in-network, 20.5% of the operations led to an out-of-network bill.