ASC vs. HOPD billing looks similar on the surface, since both settings perform outpatient surgery. Underneath, the rules differ in almost every way that matters for a facility claim: the payment system, the claim form, the list of payable procedures, the way Medicare pays for implants and the modifiers that explain an unusual case. When a high-cost implant claim rejects, one of those differences is the first place to look.
Quick answer: An ambulatory surgery center bills Medicare on the professional claim format (CMS-1500 or 837P) under the ASC payment system, and only for procedures on the ASC Covered Procedures List. A hospital outpatient department bills on the UB-04 (837I) under OPPS with revenue codes. Both must report device HCPCS codes correctly and use modifiers 73 and 74 for discontinued cases.
Key takeaways
- Different claim forms: Medicare ASC facility claims use the CMS-1500 format; HOPD claims use the UB-04, also known as Form CMS-1450.
- The CPL decides ASC payment: A procedure missing from the ASC Covered Procedures List does not pay in an ASC, even if it pays in a hospital.
- Devices change payment: Device-intensive procedures and pass-through device C-codes need exact device reporting.
- Discontinued cases use 73 or 74: The timing of anesthesia decides which modifier applies and how much pays.
- SG is payer-specific: Medicare stopped requiring modifier SG for ASC facility claims in 2008, but some other payers still ask for it.
ASC vs. HOPD Billing: The Core Differences
Medicare pays ambulatory surgical centers under the ASC payment system and hospital outpatient departments under the Outpatient Prospective Payment System (OPPS). The two systems share many relative weights, but they differ in what they cover, how they bundle and how claims flow. The table below summarizes the key points for ASC vs. HOPD billing.
| Area | ASC (Medicare) | HOPD (Medicare) |
|---|---|---|
| Payment system | ASC payment system | OPPS with APCs and status indicators |
| Claim form | CMS-1500 / 837P | UB-04 (Form CMS-1450) / 837I |
| Payable procedures | Only codes on the ASC Covered Procedures List | Codes payable under OPPS, outside the inpatient-only list |
| Revenue codes | Not used on the Medicare ASC claim | Required, such as 0360 for OR services and 0278 for implants |
| Device reporting | Device HCPCS for device-intensive and pass-through cases | Device HCPCS plus implant revenue codes |
Commercial and Medicaid payers do not always follow Medicare. Some ask ASCs to bill on the UB-04 with a facility bill type, and some still require modifier SG. Therefore, keep a payer grid for claim form, bill type and modifier rules before you build charge templates.
The CMS ASC Covered Procedures List (CPL)
The CMS ASC Covered Procedures List (CPL) names the surgical procedures Medicare pays when an ASC performs them. CMS updates it every year in the OPPS and ASC final rule. For 2026, CMS finalized an expansion of the ASC list and began phasing out the inpatient-only list, as its announcement of the CY 2026 hospital outpatient and ASC rule explains.
Even so, a procedure that pays in a hospital outpatient department may not pay in an ASC. Before scheduling, check the current ASC addenda for the procedure code, its payment indicator and any device-intensive flag. Doing this at scheduling, not at billing, prevents CPL denials. It also gives the surgeon time to move the case to the hospital if the ASC cannot bill it.
Device-Intensive Procedures in ASC vs. HOPD Billing
CMS flags a procedure as device-intensive when the cost of the implanted device makes up a large share of the procedure's total cost. For those procedures, the payment includes a device portion, and the claim must report the device the surgeon implanted. In practice, device-intensive procedure unbundling causes two kinds of errors:
- Billing the implant on its own line when the procedure payment already includes it, which leads to bundling denials.
- Leaving the device code off the claim, which can trigger an edit or a reduced payment.
In addition, manufacturer credits matter. If the facility gets a device at no cost or with a full or partial credit, Medicare rules require specific reporting so that Medicare reduces the device portion. Track credits with your materials team so the claim matches the invoice.
Pass-Through Device C-Codes in ASC vs. HOPD Billing
Pass-through device C-codes are HCPCS Level II codes for new devices that CMS pays separately for a limited period, on top of the procedure payment. In an HOPD claim, they carry their own status indicator and line. In an ASC claim, CMS pays the qualifying device separately as well, as long as the facility reports the C-code on its own line with the procedure.
- Confirm pass-through status for the date of service, since the status expires after a set period.
- Report the C-code and units that match the implant log and the invoice.
- Link the device to the procedure performed on the same claim.
- Stop billing the C-code separately once its pass-through status ends, because the cost then moves into the procedure payment.
Tip: Build an implant log that captures the device name, manufacturer, lot, HCPCS code and cost at the point of use. Then reconcile it with the charge before the claim leaves.
Modifier 73 and Modifier 74 for Discontinued ASC Procedures
Modifier 73 and modifier 74 explain why a facility claim shows a procedure that was not finished. The difference is the timing of anesthesia. A Medicare contractor's page on modifiers for ambulatory surgical centers describes the payment effect for ASCs:
| Modifier | When it applies | Medicare ASC payment |
|---|---|---|
| 73 | Case stopped after staff prepared the patient in the room, but before anesthesia | About half the procedure payment |
| 74 | Case stopped after anesthesia started or the procedure began | Full procedure payment |
| 52 | Discontinued procedure that does not need anesthesia | Reduced payment |
Device-intensive procedures need extra care when a case stops. If the facility opened a device before stopping, check the current CMS instructions for how the device portion pays, and document whether the team implanted, opened or returned the device.
Modifier SG and Other Payer-Specific Rules
Modifier SG once identified ASC facility services on Medicare claims. Medicare dropped that requirement when it revised the ASC payment system in 2008, so Medicare ASC claims no longer need it. However, some Medicaid programs and commercial plans still ask for SG or for a facility bill type. Keep those rules in your payer grid rather than in the general template.
UB-04 / Form CMS-1450 Institutional Billing for HOPDs
Hospital outpatient departments bill surgery on the UB-04, the paper version of Form CMS-1450, or its electronic 837I format. Each line needs a revenue code, a HCPCS code where required, units and charges. For implant cases, hospitals report the implant under revenue code 0278 with its device HCPCS code, and the operating room time under 0360.
Many surgical procedures in an HOPD fall under comprehensive APCs, which pay one amount for the main procedure and most items on the claim. As a result, a missing device code or a wrong revenue code can affect the whole claim, not just one line. Strong charge capture at the point of care keeps the claim complete.
ASC Payment Rules That Change the Facility Fee
Three Medicare rules shape what an ASC receives, and none of them works the same way under OPPS.
- Payment indicators: ASC addenda use payment indicators, not OPPS status indicators. For instance, J8 marks a device-intensive procedure, and N1 marks a packaged item with no separate payment.
- Device-intensive threshold: Under 42 CFR 416.171, a procedure qualifies as device-intensive when its HCPCS code-level device offset is greater than 30 percent.
- Multiple procedures: Under 42 CFR 416.172, the procedure with the highest rate pays at 100 percent. Other covered procedures in the same session that are subject to the discount pay at 50 percent.
On the hospital side, an HOPD reports outpatient surgery on a type of bill 13X claim. Therefore, set the bill type in the HOPD charge template and keep it out of the ASC one.
Example: ASC vs. HOPD Billing for the Same Implant Case
Consider a hypothetical knee procedure with an implant that Medicare lists as device-intensive and payable in both settings. In the ASC, the facility bills Medicare on the 837P with the procedure code and the device HCPCS code, without revenue codes. In the HOPD, the hospital bills on the 837I with revenue codes for the operating room and the implant, the procedure code and the device code. If the surgeon stops the case after anesthesia because of a complication, both settings append modifier 74 and document the reason.
Professional Claims in ASC vs. HOPD Billing
The surgeon's professional claim follows its own rules in both settings. In ASC vs. HOPD billing, the main difference on the professional side is the place of service code. The surgeon reports place of service 24 for an ambulatory surgical center, 22 for an on-campus hospital outpatient department and 19 for an off-campus department.
In each case, Medicare pays the surgeon at the facility rate, since the facility bills separately for the room, staff and supplies. Consequently, a wrong place of service code can lead to an overpayment, a denial or a mismatch between the professional and facility claims. Check that the scheduling system sends the right location to both billing teams, and audit a sample of cases each month to confirm the codes match.
Anesthesia, pathology and imaging providers also bill professional claims for the same case. Their place of service must match the facility as well, so share the case location with every group that bills for it.
Preventing Denials in ASC vs. HOPD Billing
The causes below lead to facility denials on implant cases. A pre-bill review should check each one:
- Procedure missing from the ASC Covered Procedures List for the date of service.
- Device code missing, or a pass-through C-code billed after its status ended.
- Implant billed separately when the procedure payment already includes it.
- Modifier 73 or 74 missing or chosen without documented anesthesia timing.
- Wrong claim form, bill type or payer-specific modifier for a commercial plan.
Orthopedic and spine cases carry the highest implant costs, so review them first. Our guide to orthopedic coding challenges covers the professional side of the same cases.
Get Help With ASC vs. HOPD Billing
ASC vs. HOPD billing rewards facilities that check the CPL, log every device and match each claim to the setting and payer. For ASC-specific support, see our ASC billing services. For broader help, our comprehensive medical coding and RCM solutions cover facility coding, device reconciliation and denial follow-up.
Stop losing money on implant cases
Dr Biller RCM codes ASC and hospital outpatient claims, reconciles devices and works facility denials.
Frequently Asked Questions
No. Medicare ASC facility claims use the CMS-1500 format or the 837P. Some commercial and Medicaid payers ask ASCs to bill on the UB-04, so check each contract.
Not for Medicare ASC claims since 2008. Some other payers still require it, so follow each payer's rules.
Modifier 73 applies when the case stops before anesthesia starts. Modifier 74 applies when it stops after anesthesia starts or after the procedure begins.
Medicare will not pay the ASC facility fee for it. Check the current list before scheduling the case.
Place of service 24. A surgeon working in a hospital outpatient department uses 22 for an on-campus location or 19 for an off-campus location.
It is a HCPCS code for a new device that Medicare pays separately for a limited time, on top of the procedure payment.
