Overview
An Ambulatory Surgery Center (ASC) is a Medicare-certified freestanding or hospital-affiliated outpatient facility specializing in surgical procedures that do not require hospital admission. ASCs perform elective, planned procedures where the patient arrives, has surgery, recovers briefly, and discharges home — typically within a few hours. Examples include cataract surgery, cosmetic procedures, endoscopy, carpal tunnel release, many orthopedic arthroscopic procedures, and increasingly joint replacement and spinal procedures moving from hospital to ASC.
ASC payment follows the Medicare Ambulatory Surgical Center Payment System (ASC PS), distinct from the Hospital Outpatient Prospective Payment System (OPPS) and the Medicare Physician Fee Schedule (MPFS). The ASC PS pays a bundled facility fee for the procedure, plus separately billable implants, drugs, and devices when they exceed a "packaging threshold." The professional fee (surgeon, anesthesiologist) is billed separately through the MPFS and paid at site-of-service differential rates when the service is performed in an ASC.
The ASC Covered Procedures List (ASC CPL) specifies which CPT codes Medicare pays in the ASC setting. CMS updates the CPL annually; the 2025 list expanded to include total knee and hip arthroplasty moving from OPPS-only to both OPPS and ASC. Site-of-service shift has been a major CMS policy direction, accelerated by the Bipartisan Budget Act requirements and CMS's site-neutral initiatives.
Commercial and Medicaid ASC payment follows various methodologies. Many commercial payers use ASC-specific fee schedules or percentage-of-Medicare bases; some bundle more aggressively than Medicare. State Medicaid ASC payment varies substantially. High-volume ASCs negotiate directly with payers on procedure-specific fees, especially for high-cost implants.
For RCM, ASC billing has specific characteristics: (1) distinct billing claim form (CMS-1500 for professional, UB-04 for ASC facility in some states); (2) ASC-specific CPT modifiers (SG, TC exclusions); (3) packaging rules that require careful implant/drug tracking; (4) professional-facility claim coordination between surgeon group and ASC; (5) patient financial responsibility with high deductibles and copays that require point-of-service collection.
ASC ownership structures affect operations. Hospital-owned ASCs (often structured as hospital outpatient departments) bill under OPPS with hospital-outpatient rates. Freestanding ASCs (many physician-owned) bill under the ASC PS. Joint ventures between hospitals and physician groups create hybrid structures. Each structure has different payment, compliance, and RCM implications.
ASC quality reporting is mandatory for Medicare-participating ASCs. ASC Quality Reporting (ASCQR) Program measures include patient burn, falls, return to hospital, normothermia maintenance, and procedure-specific clinical outcomes. Reporting drives 2% payment adjustments. Hospital Outpatient Quality Reporting (OQR) applies to hospital-based outpatient surgery.
The economic case for ASCs is significant. CMS data consistently shows ASC payment at 60–70% of equivalent hospital outpatient payment for covered procedures. This drives growing Medicare and commercial interest in ASC utilization, provider investment in ASC capacity, and private-equity-backed ASC chain growth.
Industry benchmark
Medicare ASC Payment System (42 CFR Part 416). ASC Quality Reporting Program. ASCA (Ambulatory Surgery Center Association) industry reports.
Worked example
An ophthalmologist performs cataract surgery at a freestanding ASC. Professional claim (surgeon's claim, CMS-1500): CPT 66984-RT, site-of-service ASC (POS 24), MPFS allowable ~$550. Facility claim (ASC claim, UB-04 or state-specific): CPT 66984 with ASC PS payment ~$1,100 bundled facility fee. Total Medicare payment for the complete episode ~$1,650; compared to hospital outpatient payment where OPPS facility alone exceeds $1,700. Site-of-service shift saves Medicare and beneficiary approximately $400 per cataract procedure.
Frequently asked questions — Ambulatory Surgery Center (ASC)
What is the ASC Covered Procedures List?
The CMS-published list of CPT codes Medicare pays in the ASC setting. CMS updates it annually through the ASC payment rule. The 2025 list expanded to include total knee and hip arthroplasty, continuing the trend of high-complexity procedures moving from hospital to ASC settings.
How is ASC payment different from hospital outpatient payment?
ASCs are paid under the ASC Payment System, which pays approximately 60–70% of the equivalent hospital outpatient rate for most covered procedures. This drives site-of-service shift for covered procedures where clinical outcomes are comparable.
Can ASCs be physician-owned?
Yes. Many ASCs are physician-owned or joint ventures between hospitals and physician groups. Physician-owned ASCs are subject to Stark Law and Anti-Kickback Statute safe harbors specific to ASC ownership, including whole-hospital exception rules and bona fide ASC investment requirements.
What RCM systems support ASC billing?
ASC-specific practice management systems or modules that handle distinct ASC billing (UB-04 versus CMS-1500 depending on state), implant/drug tracking, professional-facility claim coordination, and ASC PS payment rules. Many ASCs use specialty systems distinct from hospital or physician-office PM systems.
Disclaimer
This glossary entry is operational reference for revenue-cycle and medical-billing professionals. It is not legal, clinical, or contractual advice. Industry benchmarks cite named public sources where available; always verify against the current guidance from the authority body before relying on a number in a contract, policy, or compliance filing.