Ambulatory Surgical Centers operate under a distinct Medicare reimbursement system (ASC Payment System) and require precise CPT coding for procedures and accurate ICD-10 diagnosis codes supporting medical necessity. This page covers the top diagnosis codes and surgical procedure codes used in ASC settings across the United States.
The ASC Medicare Covered Procedures List (CPL) changes annually — verify that each procedure is on the CPL before scheduling, as non-covered procedures cannot be billed to Medicare as ASC services.
Medical necessity diagnoses must directly support the procedure — a cataract surgery CPT without a documented visual impairment ICD-10 will be denied on pre-payment review.
ASCs bill the facility fee only (place of service 24); the surgeon bills separately. Do not include the surgeon’s professional fee in the ASC claim.
Modifier -74 (discontinued outpatient procedure after anesthesia) and -73 (discontinued prior to anesthesia) are ASC-specific — use them when procedures are cancelled after the patient has been prepped.
The ASC Covered Procedures List (CPL) is the annual list of procedures CMS approves for payment under the ASC Payment System. Procedures not on the list cannot be billed to Medicare as ASC services — they must be performed in a hospital outpatient department or office setting. The CPL is updated each January in the OPPS/ASC final rule.
What is place of service code for an ASC claim?
Use POS 24 (Ambulatory Surgical Center) on professional claims when a procedure is performed in an ASC. The ASC itself bills the facility fee on an institutional claim (UB-04) using POS 24 and type of bill 083x. The surgeon’s professional fee uses POS 24 on the CMS-1500.
What modifier is used for a cancelled ASC procedure?
Modifier -73 is used when a procedure is discontinued prior to administration of anesthesia (50% of the ASC payment rate is paid). Modifier -74 is used when discontinued after anesthesia has been induced (full payment). Both require documentation of the reason for cancellation.
How is colonoscopy screening vs. diagnostic coded?
Z12.11 is used for a screening colonoscopy (no symptoms, no prior history). If the colonoscopy begins as a screening but polyps are found and removed, the procedure code changes to the therapeutic colonoscopy CPT (45385), but Z12.11 remains the primary diagnosis under current CMS guidance.
How does OmniMD support ASC operations?
OmniMD’s ASC EHR includes surgical scheduling with pre-authorization tracking, anesthesia documentation, procedure CPT linking to ICD-10 diagnosis codes, and ASC-specific billing workflows with modifier management and covered procedure list verification.
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