Association for Public Policy Analysis & Management

We constructed episodes of care by matching ASC facility claims with corresponding professional claims. We defined possible surprise billing scenarios as those where patients at in-network ASCs were seen by one or more ancillary out-of-network providers whose charges were not paid in full by the insurer. We analyzed commercial claims data from the Health Care Cost Institute from 2014-2017, which includes claims from three of the nation’s five largest insurers: Humana, Aetna, and UnitedHealthcare. The analytical sample included 4.2 million ASC-based episodes of care involving 3.3 million unique patients.

One-in-ten ASC episodes involved an out-of-network ancillary professional at an in-network facility. However, the insurer paid the professionals’ billed charges in full in one-quarter (24%) of these cases, leaving no additional balance to bill the patient. After accounting for insurer payment, there was a possible surprise bill in 8% of all episodes and, among these episodes, the average balance was $1,100 per episode.

Among possible surprise bills at ASCs, most were generated by anesthesiologists (47%) and registered nurse anesthetists (CRNAs) (26%), with a smaller proportion attributable to pathologists (2%) and radiologists (1%). There was a possible surprise bill scenario 12% of the time that a CRNA provided in care at an ASC, and 8% of the time an anesthesiologist was involved in an episode. Possible surprise bills from non-ancillary physicians (e.g., gastroenterologists, otolaryngologists, ophthalmologists, and orthopedists) are much less frequent.

The prevalence of possible surprise bills was higher for fully-insured plans than self-insured plans and the average balance between charges and allowed amounts was $200 greater in fully-insured plans, which suggests that coverage is more generous in self-insured plan. The prevalence of possible surprise bills was also higher for HMOs than PPOs.

ASC utilization is increasing, and it is important to understand patients’ risk of surprise medical bills and out-of-pocket financial liability in this setting. Only six states currently protect patients from surprise bills from providers in ASCs, and these protections are limited to enrollees in fully-insured plans due to federal pre-emption of self-insured plan regulation under ERISA. This study demonstrates that future state and federal policies to address surprise medical billing should include protections for services rendered at ASCs. Additionally, our finding that professionals are paid in full in one-in-four cases demonstrates that studies identifying surprise medical billing based solely on network status may overestimate rates.