What Is APC (Ambulatory Payment Classification)?
An APC is the hospital outpatient classification system used by CMS under the Outpatient Prospective Payment System (OPPS) to group similar outpatient services for prospective payment to hospitals.
- Hospital outpatient billing turns on the OPPS payment status indicator each HCPCS code carries, not on the code alone.
- Billing a packaged service as separately payable creates compliance risk and inflates the charge; missing a line that was separately payable leaves money uncollected.
APC (Ambulatory Payment Classification)
Also known as: Ambulatory Payment Classification
An APC is the hospital outpatient classification system used by CMS under the Outpatient Prospective Payment System (OPPS) to group similar outpatient services for prospective payment to hospitals.
Definition
Implemented in 2000, the APC system is the outpatient analog to the inpatient DRG system. CMS groups outpatient services that are comparable clinically and in resource use into APC groups and assigns each group a relative weight, and the OPPS payment rate for a service is that relative weight multiplied by the conversion factor (42 CFR 419.31 and 419.32, ecfr.gov), before the adjustment for area wage differences. It is not the case that every code on a hospital outpatient claim earns its own APC payment. A long list of items and services is packaged or conditionally packaged into the payment for the procedure they support — operating, procedure and recovery room use, observation, anesthesia, most supplies and implantable devices, image guidance, and certain clinical diagnostic laboratory tests among them (42 CFR 419.2(b)) — and a separate list of services is excluded from OPPS altogether, including physician professional services, therapy services paid on the outpatient therapy fee schedule, ambulance, take-home durable medical equipment and mammography (42 CFR 419.22). Some APCs go further and use 'comprehensive APC' (C-APC) bundling, where the ancillary services on the claim are folded into a single payment for the primary procedure. APC assignments and rates are set annually in the OPPS Final Rule and refreshed quarterly in the OPPS addenda. APCs apply to hospital outpatient departments, including hospital-based clinics, but not to physician professional services or ASCs (which have their own ASC payment system).
Example
CPT 92928 (percutaneous coronary stent placement, single major coronary artery or branch) performed in a hospital outpatient cath lab is assigned to a comprehensive APC, so the procedure, contrast, supplies, device and most ancillaries on that claim resolve to one payment rather than to separate paid lines. The arithmetic here is synthetic — the weight and the conversion factor are round placeholders chosen to show the formula, not published CMS values: a relative weight of 50.0000 at a conversion factor of $100.00 gives 50.0000 × $100.00 = $5,000.00 before the area wage adjustment and before beneficiary coinsurance. For the real figures in a given year, read the OPPS addenda rather than a secondhand table — Addendum A lists the APCs and their rates, Addendum B lists payment and status indicator by HCPCS code, and both are reposted each quarter at cms.gov (checked 17 September 2026). The same procedure performed in a hospital inpatient setting is paid via MS-DRG instead.
Common Misconceptions
APCs apply only to the hospital's facility fee on hospital outpatient claims (UB-04), not to the physician's professional fee for the same encounter. The physician's professional fee for the same procedure is paid separately under the MPFS using RVUs.
Practical Application
Hospital outpatient billing turns on the OPPS payment status indicator each HCPCS code carries, not on the code alone. The indicator is what decides whether a line is paid separately under OPPS, packaged into the payment for another service on the same claim, conditionally packaged depending on what else is billed, or not payable under OPPS at all. Those assignments move: the per-code assignment is published in Addendum B for each quarter, and the indicator definitions are published in Addendum D1 of each year's OPPS final rule, so check the current addenda rather than working from a remembered letter. Billing a packaged service as separately payable creates compliance risk and inflates the charge; missing a line that was separately payable leaves money uncollected.
Related Terms
DRG (Diagnosis-Related Group)
A DRG is the inpatient hospital classification system that groups admissions with similar clinical characteristics and resource use into a single payment category; CMS uses MS-DRGs to pay hospitals under the IPPS for Medicare inpatient stays.
Read definitionCPT (Current Procedural Terminology)
CPT is the five-digit procedural code set developed and maintained by the American Medical Association that describes medical, surgical, and diagnostic services performed by physicians and qualified health professionals; it is HIPAA-named for use in claims.
Read definitionUB-04 form
The UB-04 (also known as CMS-1450) is the standard paper claim form used by institutional providers (hospitals, SNFs, home health, hospice) to bill Medicare and other payers; its electronic equivalent is the 837I (Institutional) HIPAA EDI transaction.
Read definitionCMS
CMS is the federal agency within the U.S. Department of Health and Human Services that administers Medicare, jointly administers Medicaid and CHIP with the states, and oversees the Health Insurance Marketplaces and HIPAA administrative simplification.
Read definitionWhere This Applies on MedPrecision
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