Healthcare Data Glossary

An Accountable Care Organization (ACO) is a group of doctors, hospitals, and other health care providers who voluntarily coordinate care for Medicare beneficiaries with the goal of delivering high-quality, efficient care. ACOs accept accountability for total cost and quality of care for an attributed patient population. Under the Medicare Shared Savings Program (MSSP), ACOs that reduce spending below a benchmark while meeting quality thresholds share in the savings. CMS administers multiple ACO models; in 2024, ACOs served over 11 million Medicare beneficiaries.

An Ambulatory Surgical Center (ASC) is a Medicare-certified health care facility that provides surgical services to patients who do not require hospitalization. CMS certifies ASCs under Conditions for Coverage and reimburses them under the ASC Payment System. CMS publishes quality and performance data for over 5,600 Medicare-certified ASCs through the Care Compare ASC dataset. Common ASC procedures include cataract surgery, colonoscopies, and orthopedic procedures. ASCs collectively perform more than 23 million procedures annually in the United States.

Balance billing is the practice by which an out-of-network provider bills a patient for the difference between the provider's charge and the amount the patient's insurer pays — the 'balance'. The No Surprises Act prohibits balance billing in specified circumstances: emergency services, air ambulance transport, and non-emergency services at in-network facilities when the patient had no prior informed choice of provider. Medicare and Medicaid programs have long-standing limits on provider balance billing.

The CMS Certification Number (CCN) is a six-digit identifier assigned by CMS to Medicare- and Medicaid-certified health care facilities, including hospitals, nursing homes, home health agencies, hospices, dialysis facilities, and ambulatory surgical centers. The CCN is the primary facility identifier in CMS administrative data and the linking key between datasets such as Care Compare, the Provider of Services (POS) file, and HCRIS cost reports. The first two digits encode state; the remaining four identify the facility within that state and encode its facility type.

The Centers for Medicare & Medicaid Services (CMS) is a federal agency within the U.S. Department of Health and Human Services that administers Medicare, Medicaid, the Children's Health Insurance Program (CHIP), and the Health Insurance Marketplace. CMS sets standards for health care quality, payment policy, and provider enrollment. The agency manages key public data systems including NPPES, PECOS, Care Compare, Open Payments, and the Quality Payment Program, and publishes provider, facility, and claims data used in health services research.

CMS Care Compare is a publicly accessible data resource that provides quality and performance information for Medicare-participating health care providers and facilities — including hospitals, nursing homes, home health agencies, hospices, dialysis facilities, ambulatory surgical centers, and clinicians. CMS launched Care Compare in 2020, consolidating previously separate comparison tools (Hospital Compare, Nursing Home Compare, Home Health Compare, and others) into a unified platform. Data includes star ratings, inspection results, staffing levels, and quality measures.

CMS Star Ratings are quality scores assigned to Medicare-participating providers, facilities, and health plans on a scale of 1 to 5 stars to help beneficiaries compare quality of care. Separate rating systems exist for nursing homes (Overall, Health Inspections, Staffing, and Quality Measures domains), home health agencies, dialysis facilities, hospices, and Medicare Advantage plans. Ratings are calculated from inspection results, staffing data, and quality measures reported to CMS. Methodologies are published annually in CMS technical documentation.

Current Procedural Terminology (CPT) codes are a proprietary set of medical codes maintained by the American Medical Association (AMA) that describe medical, surgical, and diagnostic procedures and services. CPT codes are required under HIPAA for reporting outpatient procedures on insurance claims. Each five-character code maps to a specific procedure. CMS assigns Relative Value Units (RVUs) to CPT codes in the Medicare Physician Fee Schedule, which determines physician payment rates.

A Diagnosis Related Group (DRG) is a patient classification system that groups similar hospital inpatient cases into categories that are clinically coherent and resource-intensive. CMS uses Medicare Severity DRGs (MS-DRGs) to determine prospective payment amounts for hospital inpatient stays under Medicare Part A through the Inpatient Prospective Payment System (IPPS). Each DRG is assigned a relative weight representing average resource consumption. Hospitals receive a fixed payment per DRG regardless of actual costs.

The EDI 837 is a HIPAA-standard electronic data interchange format for submitting health care claims. Three transaction sets exist: 837P (Professional, based on CMS-1500), 837I (Institutional, based on UB-04), and 837D (Dental). Maintained by ASC X12 and implemented under HIPAA Administrative Simplification, the 837 replaced paper claims for covered transactions. Clearinghouses translate provider billing software output into X12 837 format for payer submission. CMS requires the 837 for all Medicare claims.

An Electronic Health Record (EHR) is a digital version of a patient's medical chart that is real-time, patient-centered, and accessible to authorized users across health care settings. EHRs contain medical history, diagnoses, medications, treatment plans, immunization records, allergies, radiology images, and laboratory results. Under the HITECH Act and ONC's Health IT Certification program, EHR adoption expanded substantially after 2009. EHRs differ from Electronic Medical Records (EMRs) in that EHRs are designed for cross-organizational information sharing.

An Electronic Remittance Advice (ERA) is a HIPAA-standard electronic document (ASC X12 835 transaction) that a health care payer sends to a provider explaining payment decisions on submitted claims. ERAs specify which services were paid, denied, or adjusted and include standardized reason codes. Under HIPAA, payers must transmit ERAs to providers who request them electronically. ERA data is the primary mechanism for providers to reconcile Medicare and commercial insurance payments in accounts receivable management systems.

End-Stage Renal Disease (ESRD) is permanent, complete kidney failure that requires dialysis or a kidney transplant to maintain life. ESRD is the only condition — regardless of age — that qualifies individuals for Medicare solely on the basis of diagnosis. Medicare ESRD coverage begins the fourth month of dialysis treatment or upon kidney transplant. CMS tracks dialysis facility quality through the ESRD Quality Incentive Program (QIP) and publishes facility performance data on Care Compare. In 2024, approximately 808,000 patients receive ESRD treatment in the United States.

An Explanation of Benefits (EOB) is a document sent by a health insurer to a covered member and provider after a claim is processed, explaining what services were billed, what the plan paid, what was denied, and what the member may owe. EOBs are not bills; they are informational summaries. Under the CMS Interoperability and Patient Access Final Rule, Medicare Advantage and Medicaid plans must make EOB and claims data available to beneficiaries through FHIR-based Patient Access APIs, enabling members to retrieve their claims history electronically.

Fast Healthcare Interoperability Resources (FHIR) is a standard for health care data exchange developed by HL7 International. FHIR defines modular data elements — resources such as Patient, Practitioner, Organization, and Observation — exchangeable via REST APIs, JSON, and XML using standard web technologies. The ONC 21st Century Cures Act Final Rule mandated FHIR-based APIs for certified EHRs starting in 2022. FHIR R4 is the current base standard for U.S. health care interoperability.

A Federally Qualified Health Center (FQHC) is a community-based health care provider that receives funding from the HRSA Health Center Program to provide primary care services to medically underserved areas and populations. FQHCs must serve all patients regardless of ability to pay and offer a sliding-fee discount schedule. Under Medicare and Medicaid, FQHCs receive an enhanced prospective payment rate. As of 2024, approximately 1,400 HRSA-funded health center grantees operate over 15,000 service delivery sites serving nearly 31 million patients annually.

The Healthcare Common Procedure Coding System (HCPCS) is a standardized coding system used to identify health care services, supplies, products, and equipment for billing in Medicare, Medicaid, and other programs. HCPCS Level I codes are AMA CPT codes; HCPCS Level II codes are alphanumeric codes maintained by CMS covering durable medical equipment, prosthetics, orthotics, supplies, drugs, and other items not covered by CPT. CMS publishes the HCPCS Level II code set annually.

The Healthcare Cost Report Information System (HCRIS) is a CMS database of annual cost reports submitted by Medicare-participating health care facilities — including hospitals, nursing homes, home health agencies, and others. Cost reports capture detailed financial and operational data including total charges, total costs, number of beds, staffing hours, and Medicare utilization. HCRIS data is publicly available and forms the basis for research on hospital financial health, profit margins, and cost structure. CMS releases quarterly HCRIS file updates; historical data extends to the 1990s.

The Health Insurance Portability and Accountability Act of 1996 (HIPAA) is a federal law that established national standards for the privacy and security of individually identifiable health information and for electronic health care transactions. HIPAA's Administrative Simplification provisions mandate standard transaction formats (including NPI), require privacy protections for Protected Health Information (PHI), and establish security safeguards for electronic PHI. HHS's Office for Civil Rights enforces the HIPAA Privacy and Security Rules.

Health Level Seven International (HL7) is an accredited standards development organization that creates frameworks and standards for health information technology. HL7 develops messaging standards (HL7 v2.x), clinical document standards (C-CDA / CDA), and the modern FHIR interoperability standard. The name 'Level Seven' refers to the seventh layer of the ISO OSI model — the application layer. HL7 v2 messages remain the most widely deployed health care data exchange format in hospital information systems globally.

A Health Professional Shortage Area (HPSA) is a geographic area, population group, or facility designated by HRSA as having a shortage of primary medical care, dental, or mental health providers. HPSA designations trigger eligibility for National Health Service Corps scholarships and loan repayment and enhanced Medicare payment rates (+10% for primary care in geographic HPSAs). HRSA uses a scoring system based on provider-to-population ratios, distance to nearest care source, and percentage of population below 100% of the federal poverty level.

The Health Resources and Services Administration (HRSA) is a federal agency within HHS that improves health care access to people who are geographically isolated or economically or medically vulnerable. HRSA programs include the Health Center Program (FQHCs), the National Health Service Corps, and the Ryan White HIV/AIDS Program. HRSA also designates Health Professional Shortage Areas (HPSAs) and Medically Underserved Areas (MUAs) and publishes the Uniform Data System (UDS) — an annual dataset of FQHC performance and patient demographics.

ICD-10 is a medical coding system used to classify diagnoses, symptoms, and medical procedures. The World Health Organization maintains ICD-10 globally; the United States uses two adaptations — ICD-10-CM (Clinical Modification) for diagnoses, maintained by the CDC, and ICD-10-PCS (Procedure Coding System) for inpatient procedures, maintained by CMS. ICD-10 replaced ICD-9 for U.S. HIPAA transactions in October 2015. ICD-10-CM contains over 70,000 diagnosis codes used on all HIPAA-covered claims.

The List of Excluded Individuals/Entities (LEIE) is a database maintained by the HHS Office of Inspector General (OIG) of individuals and entities barred from participation in Medicare, Medicaid, and all other federal health care programs. Exclusions result from convictions for fraud, patient abuse, licensing revocations, or other statutory bases. Organizations that employ or contract with excluded parties face significant civil monetary penalties. The LEIE is updated monthly and available as a free bulk CSV download from oig.hhs.gov.

A Machine-Readable File (MRF) is a structured data file published by hospitals and health insurers under federal price transparency regulations. Under the CMS Hospital Price Transparency Rule (effective January 2021), hospitals must publish an MRF containing standard charges for all items and services. Under the Transparency in Coverage Rule (effective July 2022), group health plans must publish MRFs containing in-network negotiated rates and out-of-network allowed amounts. MRFs are typically published in JSON or CSV format and must be publicly accessible without authentication.

The Medicare Access and CHIP Reauthorization Act of 2015 (MACRA) is a federal law that repealed the Sustainable Growth Rate (SGR) formula for Medicare physician payment and established the Quality Payment Program. MACRA created MIPS and Advanced APMs as the two pathways for clinician participation, shifted Medicare payment toward value-based models, and mandated interoperability requirements for EHRs. MACRA was signed into law on April 16, 2015. CMS began collecting MIPS performance data under MACRA in January 2017.

Medicaid is a joint federal-state health insurance program that provides coverage to low-income individuals and families, including children, pregnant women, elderly adults, and people with disabilities. Authorized by Title XIX of the Social Security Act, Medicaid is administered by states within federal guidelines. CMS oversees federal Medicaid policy and matching payments. In 2024, Medicaid and CHIP combined covered approximately 90 million individuals, making it the largest source of health insurance coverage in the United States.

Medicare is the federal health insurance program administered by CMS for people age 65 or older, certain younger individuals with disabilities, and people with End-Stage Renal Disease. Established by Title XVIII of the Social Security Act in 1965, Medicare covers inpatient hospital care (Part A), outpatient and physician services (Part B), prescription drugs (Part D), and managed care alternatives (Part C / Medicare Advantage). In 2024, Medicare covered approximately 67 million beneficiaries.

Medicare Advantage (Part C) is an alternative to traditional Medicare in which private health plans — approved and paid by CMS — deliver all Medicare-covered benefits plus optional supplemental benefits such as vision, dental, and hearing. CMS reimburses Medicare Advantage plans through risk-adjusted capitation payments. CMS publishes plan performance data including star ratings, enrollment figures, and quality metrics. In 2024, approximately 33 million Medicare beneficiaries — more than 50% of total Medicare enrollment — are enrolled in Medicare Advantage plans.

The Merit-Based Incentive Payment System (MIPS) is a CMS value-based payment program under the Quality Payment Program that adjusts Medicare clinician reimbursement based on performance across four categories: Quality, Promoting Interoperability, Improvement Activities, and Cost. MIPS applies to eligible clinicians — physicians, nurse practitioners, physician assistants, and others — who meet Medicare volume thresholds. Scores range from 0 to 100; high performers receive positive payment adjustments and low performers receive negative adjustments. MIPS was established under MACRA in 2015.

The No Surprises Act (Division BB of the Consolidated Appropriations Act, 2021) is a federal law effective January 1, 2022, that protects patients from unexpected out-of-network bills in specified circumstances. The law limits patient cost-sharing to in-network rates for emergency services, air ambulance services, and non-emergency care at in-network facilities when the patient had no informed choice of provider. It also established an independent dispute resolution (IDR) process for payment disputes between insurers and providers.

The National Provider Identifier (NPI) is a unique, 10-digit numeric identifier assigned to health care providers in the United States under HIPAA Administrative Simplification. Administered by CMS through NPPES, an NPI is permanent and does not change when a provider changes their name, address, or taxonomy. All HIPAA-covered health care providers must obtain an NPI for use in administrative and financial transactions, including claims, eligibility inquiries, and remittance advice.

The National Plan and Provider Enumeration System (NPPES) is the CMS database that assigns and maintains National Provider Identifiers. Health care providers apply for NPIs through NPPES, which collects provider names, practice locations, and taxonomy codes. NPPES data is publicly downloadable as a monthly bulk file and is also accessible through the NPI Registry API. The system enumerates both individual providers (Type 1 NPI) and organizations (Type 2 NPI) across all U.S. health care settings.

The National Uniform Claim Committee (NUCC) is a voluntary organization led by the American Medical Association that maintains the standard professional claim form (CMS-1500) and the Healthcare Provider Taxonomy code set used in HIPAA administrative transactions. NUCC taxonomy codes identify a provider's type, classification, and specialization for purposes of NPI enumeration and claim processing. NUCC publishes taxonomy code updates annually. The complete NUCC taxonomy code set is publicly available and is the authoritative source for all taxonomy codes stored in NPPES.

An OIG exclusion is a formal administrative sanction imposed by the HHS Office of Inspector General that prohibits an individual or entity from participating in Medicare, Medicaid, and all other federally funded health care programs. Mandatory exclusions are required by statute — for example, felony convictions for health care fraud. Permissive exclusions are at the OIG's discretion. Excluded parties cannot receive federal program payment directly or through an employer. Exclusion records are published in the LEIE.

CMS Open Payments is a national disclosure program established by the Physician Payments Sunshine Act that collects and publishes information about financial relationships between drug and device manufacturers and applicable physicians, teaching hospitals, and other health care providers. Manufacturers and group purchasing organizations (GPOs) report payments and transfers of value — including consulting fees, research grants, meals, travel, and royalties — to CMS annually. Open Payments data is publicly searchable at openpaymentsdata.cms.gov.

The Payroll-Based Journal (PBJ) is a CMS system requiring nursing homes and long-term care facilities to submit direct care staffing data electronically on a quarterly basis. Mandated under the Affordable Care Act and the SNF Staffing Final Rule, PBJ data includes actual hours worked by nursing staff by day, job type, and hire type (employee vs. contract staff). CMS uses PBJ data to calculate the Staffing Rating component of nursing home star ratings on Care Compare. PBJ data is publicly available and widely used in nursing home staffing research.

The Provider Enrollment, Chain, and Ownership System (PECOS) is the CMS enrollment database for Medicare providers and suppliers. PECOS stores enrollment records for practitioners, group practices, and suppliers who have applied to participate in Medicare. The system records enrollment status, effective dates, practice locations, and reassignment of billing rights. The PECOS Public Extract (PPEF) is a periodically released public file enabling external verification of Medicare enrollment status by NPI.

Protected Health Information (PHI) is any individually identifiable health information held or transmitted by a HIPAA covered entity or business associate, in any form or medium. PHI includes diagnoses, treatment records, payment information, and any data that could identify the individual — name, address, dates of service, Social Security number, and 16 other identifiers enumerated in the HIPAA Privacy Rule. De-identified information that cannot reasonably be used to identify an individual is not PHI and falls outside HIPAA's Privacy Rule protections.

Prior authorization is a requirement by a health insurer that a provider obtain approval before delivering certain services, procedures, or medications for them to qualify for reimbursement. Used to manage utilization and cost, prior authorization has been associated with treatment delays and administrative burden. The CMS Interoperability and Prior Authorization Final Rule (CMS-0057-F) requires payers to implement FHIR-based APIs for electronic prior authorization beginning in 2027 for Medicare Advantage, Medicaid, and CHIP plans.

Provider enrollment is the process by which health care providers and suppliers apply for and maintain participation in Medicare, Medicaid, or other federal health care programs. CMS manages Medicare enrollment through PECOS. Providers submit CMS-855 forms (or online equivalents) to apply, revalidate, or update enrollment records. Enrolled providers receive a PTAN from their Medicare Administrative Contractor. CMS may revoke, deny, or bar enrollment for fraud, OIG exclusion, or failure to meet program standards.

A Provider Transaction Access Number (PTAN) is an identifier assigned by a Medicare Administrative Contractor (MAC) to individual providers or supplier organizations upon Medicare enrollment. Unlike the NPI, which is universal, a PTAN is jurisdiction-specific — issued by the MAC serving a provider's geographic area. PTANs appear on Medicare remittance advice and are required for electronic eligibility transactions. A single NPI holder may have multiple PTANs when enrolled in multiple MAC jurisdictions or under different provider types.

The Quality Payment Program (QPP) is a CMS framework established by MACRA that replaced the Sustainable Growth Rate (SGR) formula for Medicare clinician reimbursement. QPP offers two participation pathways: MIPS (Merit-Based Incentive Payment System) and Advanced Alternative Payment Models (APMs). Eligible clinicians choose a pathway based on practice size, specialty, and patient volume. QPP ties Medicare payment rates to quality and value metrics. CMS publishes individual and group QPP performance scores as public data accessible through qpp.cms.gov.

A Skilled Nursing Facility (SNF) is a Medicare-certified inpatient facility that provides skilled nursing care, physical therapy, occupational therapy, and speech-language pathology services. Medicare Part A covers SNF stays after a qualifying three-day inpatient hospital stay. CMS reimburses SNFs under the Patient-Driven Payment Model (PDPM). SNF quality data — including staffing levels, inspection results, and quality measures — is published on CMS Care Compare. In 2024, over 15,000 SNFs are certified to participate in Medicare.

The Physician Payments Sunshine Act (Section 6002 of the Affordable Care Act) requires applicable manufacturers and group purchasing organizations to report to CMS all payments or transfers of value made to physicians and teaching hospitals. CMS collects and publicly discloses this data through the Open Payments program. The law was enacted to increase transparency about financial relationships between health care industry and practitioners. Reportable transfers include research payments, honoraria, entertainment, consulting fees, gifts, and speaker program payments.

A healthcare provider taxonomy code is a 10-character alphanumeric code that classifies a provider's type, classification, and specialization. Maintained by the National Uniform Claim Committee (NUCC), taxonomy codes are used in HIPAA transactions and stored in NPPES alongside each NPI record. A provider may have multiple taxonomy codes, with one designated as primary. The code structure groups providers hierarchically: individuals, non-individual practitioners, and suppliers, each subdivided by specialty.

A Type 1 NPI is a National Provider Identifier assigned to individual health care providers — persons who render or provide health care services or supplies. Physicians, dentists, nurses, pharmacists, and other licensed practitioners hold Type 1 NPIs. An individual provider receives only one Type 1 NPI regardless of how many locations they practice in or organizations they belong to. Solo practitioners who bill independently are enumerated as Type 1 under HIPAA.

A Type 2 NPI is a National Provider Identifier assigned to organizations — health care entities that provide health care services or supplies and have a workforce that submits claims under the organization's name. Hospitals, group practices, clinics, laboratories, and home health agencies are examples. A single organization may have multiple Type 2 NPIs for distinct subparts that file separately with Medicare. Type 2 NPIs are managed through NPPES and included in public bulk data downloads.

The Unique Physician Identification Number (UPIN) was a six-character alphanumeric Medicare identifier assigned to physicians beginning in 1984. UPINs were required on Medicare claims for referring and ordering physicians. CMS replaced UPINs with NPIs for all HIPAA-covered transactions on May 23, 2007. Although no longer used in active Medicare billing, UPINs appear in legacy Medicare claims data and historical research datasets, particularly for studies using data predating the NPI transition.

Value-based care is a health care delivery model in which providers are reimbursed based on patient health outcomes and care quality rather than the volume of services rendered. Contrasted with fee-for-service payment, value-based arrangements include quality metrics, total cost-of-care targets, and shared savings or shared risk provisions. CMS administers value-based care programs through the Innovation Center (CMMI), including Accountable Care Organizations, bundled payment models, and Primary Care First. The model aims to reduce unnecessary utilization while improving clinical outcomes.