POS 24 in medical billing is the Place of Service code used to identify services performed in a Medicare-certified Ambulatory Surgical Center (ASC).
POS 24 indicates that surgical or diagnostic care was provided in a freestanding ASC rather than in a physician’s office or hospital outpatient department, enabling CMS and commercial payers to apply the appropriate reimbursement methodology.
POS 24 is the standard coding designation for outpatient surgery, endoscopy, ophthalmology, orthopedic procedures, and other ASC-covered services under Medicare payment rules.
POS code 24 exists because payment methodology varies by setting. Medicare applies a different fee schedule depending on where a procedure is performed, so it needs a clear marker to identify the location and apply the appropriate cost-sharing rules. POS 24 is that marker.
This guide covers what POS 24 means, when to use it, how it affects payment, how it compares to POS 11, 19, 21, and 22, and how to keep claims clean under the CY 2026 rules.
What is an Ambulatory Surgical Center?
An Ambulatory Surgical Center is a distinct facility, certified by CMS under 42 CFR Part 416, that performs same-day surgery on patients who do not need overnight hospital care. The federal definition requires the expected duration of services not to exceed 24 hours following admission. The ASC must hold a Medicare agreement and meet Conditions for Coverage in Subparts B and C of Part 416.
ASCs sit between physician offices and hospitals on the care continuum. A physician’s office handles minor procedures under local anesthesia. A hospital handles complex cases, emergencies, and patients who need inpatient monitoring. An ASC handles scheduled outpatient surgery that needs an operating room, sterile environment, anesthesia support, and short post-op recovery, but no overnight stay.
The setting differs from a hospital outpatient department in three concrete ways. First, an ASC operates as its own enrolled entity with its own CMS Certification Number, not under a hospital’s provider number.
Second, an ASC bills the facility portion under the ASC Payment System, while a hospital outpatient department bills under OPPS.
Third, ASC and hospital outpatient payments are calculated under separate methodologies, so the same procedure can be reimbursed differently depending on the setting.
Common procedures performed in ASCs include cataract surgery, screening and diagnostic colonoscopy, hernia repair, carpal tunnel release, knee arthroscopy, ENT procedures such as tonsillectomy, pain management injections, and a growing list of orthopedic and cardiovascular cases.
When Should POS 24 Be Used?
Use POS 24 when face-to-face service occurs within a Medicare-certified ASC. The general CMS rule is plain: the POS reflects the actual location where the patient receives the service, not where the provider reads results or interprets a study. If the surgeon performs the procedure inside the ASC, the claim carries POS 24, regardless of where the surgeon’s main office is located.
When POS 24 clearly applies
- A gastroenterologist performs a screening colonoscopy inside a certified freestanding ASC. The surgeon’s professional claim uses POS 24. The ASC’s facility claim also uses POS 24.
- An ophthalmologist who has an ownership interest in an ASC performs cataract surgery there. Both the professional claim and the facility claim carry POS 24, even though the surgeon’s office is across the street.
- A pain management physician administers an epidural steroid injection in an ASC operating suite under fluoroscopic guidance. POS 24 applies.
When POS 24 does not apply
- The procedure happens in a hospital-owned outpatient surgery suite located on the hospital campus. That setting is POS 22, not POS 24.
- The patient is admitted to the hospital before surgery. Inpatient surgery uses POS 21.
- The surgeon performs a minor in-office excision under local anesthesia in a private practice exam room. That is POS 11.
- A hospital-affiliated off-campus outpatient surgical suite that bills under OPPS uses POS 19.
Same-day discharge requirement
The 24-hour service rule under 42 CFR 416.2 sets the outer limit. If a patient’s expected post-admission service time exceeds 24 hours, the case does not qualify as ASC care. If a complication forces an unplanned transfer to a hospital and inpatient admission, the ASC claim still reflects what was done in the ASC, and the inpatient stay is billed by the hospital under its own POS.
Which Specialties and Procedures Use POS 24 Most Often?
ASCs cluster around specialties that perform high volumes of scheduled, low-acuity surgery. The Medicare ASC Covered Procedures List (ASC-CPL) defines which CPT and HCPCS codes Medicare will pay for in an ASC.
| Specialty | Typical procedures | High-volume CPT examples |
| Ophthalmology | Cataract removal with IOL, YAG laser, glaucoma surgery | 66984, 66982, 66821 |
| Gastroenterology | Diagnostic and screening colonoscopy, upper endoscopy | 45378, 45380, 45385, 43239 |
| Orthopedics | Knee and shoulder arthroscopy, carpal tunnel release | 29881, 29827, 64721 |
| Pain management | Epidural steroid injections, facet joint injections, radiofrequency ablation | 62323, 64483, 64635 |
| Otolaryngology (ENT) | Tonsillectomy, tympanostomy tubes, sinus surgery | 42826, 69436, 31256 |
| Plastic surgery | Skin lesion excision, breast biopsy, reconstructive procedures | 11606, 19120, 19301 |
| Urology | Cystoscopy, prostate biopsy, vasectomy | 52000, 55700, 55250 |
Procedures excluded from the ASC setting
Some procedures stay off the ASC Covered Procedures List because of clinical risk or expected recovery time. Historically, CMS excluded procedures that typically require major or prolonged invasion of body cavities, involve major blood vessels, are generally emergent, or commonly require systemic thrombolytic therapy.
For CY 2026, CMS reframed these five exclusion criteria as nonbinding physician safety considerations rather than firm exclusions, which expanded the list.
The CY 2026 OPPS/ASC Final Rule (CMS-1834-FC), released November 21, 2025, added 289 procedures to the ASC-CPL based on revised criteria and added another 271 codes that were removed from the Medicare Inpatient-Only list. CMS also finalized a phase-out of the Inpatient-Only list over a three-year period, beginning with the removal of 285 mostly musculoskeletal procedures for CY 2026.
If a procedure is not on the current ASC-CPL, Medicare will not pay the facility component when billed with POS 24. Always check the current ASC Approved HCPCS Codes and Payment Rates file on the CMS website before scheduling and billing.
POS 24 vs. Other Common Place of Service Codes
The four codes most often confused with POS 24 are 11, 19, 21, and 22. The table below shows how they differ.
| POS code | Setting | Patient stay | Payment system | Typical use |
| POS 11 | Physician office | Same-day, ambulatory | Physician Fee Schedule (non-facility) | Office visits, minor in-office procedures |
| POS 19 | Off-Campus Outpatient Hospital | Same-day, no overnight | OPPS (with site-neutral adjustments) | Hospital-affiliated clinic at a separate location |
| POS 21 | Inpatient Hospital | Overnight admission | IPPS (DRG payment) | Patient admitted before or during the procedure |
| POS 22 | On-Campus Outpatient Hospital | Same-day, no overnight | OPPS | Outpatient surgery in a hospital’s main building |
Medicare Billing Rules for POS 24
Medicare’s ASC billing framework runs on three sets of rules: the ASC Payment System, the ASC Covered Procedures List, and the ASC Quality Reporting Program.
ASC Payment System
CMS sets a payment rate for each covered surgical procedure under 42 CFR 416.171. The rate combines a relative weight with the ASC conversion factor. Most facility services tied to a covered surgical procedure are bundled into one payment. That includes the operating room, nursing, drugs, most supplies, and basic equipment use. Implants and certain pass-through drugs may be paid separately when criteria are met.
Covered Procedures List
The ASC-CPL controls which procedures Medicare will pay for in an ASC. If the procedure is not on the list, Medicare denies the facility component. The list updates annually through the OPPS/ASC rulemaking cycle. The CY 2026 final rule added 289 codes from criteria changes, plus 271 codes from IPO list removal.
Documentation requirements
Documentation is the foundation of a defensible ASC claim. The operative report needs to support every line item, including modifiers, laterality, and any discontinued or reduced services. Complete, code-specific documentation is the most reliable way to keep claims clean and ready for review.
Bundled vs. separately payable
ASC payment includes most items integral to the procedure. Drug administration codes such as CPT 96360 through 96379, 96401 through 96425, and 96521 through 96523 are considered included in the ASC facility payment when reported with POS 24. Billing them separately produces denials.
Commercial Payer Considerations for POS 24
Commercial payers handle ASC claims differently from Medicare in important ways. Most commercial carriers build their ASC fee schedules off Medicare’s structure but negotiate their own rates and apply their own coverage rules.
Prior authorization
Commercial payers require prior authorization for a wider range of ASC procedures than Medicare does. Pain management injections, spine procedures, certain orthopedic surgeries, and any procedure with site-of-service review attached typically need an approved authorization before the case. A missing or expired authorization is one of the top denial reasons on commercial ASC claims.
Network and credentialing
The ASC and each rendering surgeon must be credentialed with the payer. A surgeon who is in-network for office visits may not be credentialed at the ASC under a separate tax ID. Verify both the facility’s contract and the rendering provider’s status before the case.
Common commercial denial reasons
- Procedure performed at non-participating ASC
- Missing or expired prior authorization
- Procedure not covered at ASC under the plan’s site-of-service policy
- Implant or device not separately reimbursable
- Modifier missing or used incorrectly
- Documentation does not match billed codes
How To Report POS 24 on the CMS-1500 Form
Place “24” in Box 24B on each line where the service was rendered in the ASC. Box 24B is the small two-digit field that accompanies the date of service and CPT code on each claim line. Every line must carry the correct POS, not just the first line.
Common form-entry errors
- Defaulting to POS 11 because the billing software is configured for an office setting
- Mixing POS codes across lines when the entire encounter was in the ASC
- Reporting POS 22 (on-campus hospital outpatient) for a service performed in a freestanding ASC
- Omitting Box 32, which captures the actual service facility name and address, including NPI
- Inconsistent POS between the professional and facility claims for the same encounter
Crosswalk to the UB-04
Facility claims from an ASC most often submit through the X12 837 professional format on a CMS-1500-equivalent record, not the UB-04 used by hospitals. Some hospital-operated ASCs file institutional claims, but the standard ASC bills on the professional format. Confirm payer-specific submission rules before sending.
Pre-submission checklist
- ASC certification verified for the date of service
- CPT codes confirmed on the current ASC-CPL
- POS 24 entered on every applicable line of the professional and facility claims
- Modifiers reviewed against payer rules (SG, TC, 73, 74, 50, 59, PT as applicable)
- Operative report supports each code, modifier, and unit billed
- Implants, pass-through drugs, and ancillary services billed against current payment rules
- Box 32 of CMS-1500 reflects the ASC’s name, address, and NPI
Best Practices for Accurate POS 24 Coding
Building a clean ASC coding workflow takes a small set of consistent habits.
Verify facility certification first
Before submitting any ASC claim, confirm the facility holds an active Medicare ASC agreement under 42 CFR Part 416. A lapsed certification or an unreported name change can disrupt otherwise clean claims.
Cross-check every procedure against the ASC-CPL
The ASC list changes every year, sometimes mid-year through quarterly updates. CMS posts the current Approved HCPCS Codes file on its ASC Payment page. Make it part of pre-authorization, scheduling, and pre-billing review.
Coordinate between the surgeon, the ASC, and the billing team
The professional and facility claims must agree on POS, procedure codes, modifiers, units, and date of service. Build a process where the surgeon’s coder and the ASC’s biller see each other’s claim before either is sent.
Run pre-submission audits
Pull a small sample of ASC claims each month and review POS, modifiers, documentation, and payer-specific edits. Tracking the error rate over time helps catch systematic issues early, before they affect a larger batch of claims.
Final words
POS 24 plays a central role in outpatient billing. It tells Medicare and commercial payers where a procedure happened, which determines how both the facility and professional claims are processed. Accurate reporting depends on a consistent, repeatable workflow rather than software defaults.
The CY 2026 rules expanded the ASC-CPL and gave physicians more flexibility on case selection, which adds more procedures to track. Build the workflow now: verify the ASC’s certification, check the procedure against the current ASC-CPL, enter POS 24 on every applicable line, match modifiers to payer rules, and document the case so the chart fully supports the claim.
