This document outlines common medical coding systems, providing a concise information model for each, including their purpose, category, and format.
code_category: clinical_terminology (Broader than just diagnosis, includes findings, procedures, organisms, etc.)description: A comprehensive, multilingual clinical healthcare terminology used for capturing detailed clinical information electronically. Covers diagnoses, procedures, symptoms, substances, and more.code_format: Variable-length numeric identifiers (Concept IDs), often 6 to 18 digits. Represents concepts within a complex poly-hierarchy (ontology).notes: Designed for clinical documentation and EHRs, not primarily for billing, though mappings to billing codes exist.code_category: diagnosisdescription: Used to classify and code diagnoses, symptoms, and inpatient procedures (primarily in the US). Mandated for reporting diagnoses under HIPAA.code_format:
U), followed by numbers. A decimal point follows the first 3 characters (the category). Subsequent characters provide greater specificity.S52.521A (Displaced transverse fracture of head of right radius, initial encounter for closed fracture).notes: Only the most specific codes ("leaves" of the hierarchy) are typically used for billing.code_category: procedure (specifically for inpatient hospital settings in the US)description: Used to classify and code procedures performed in US inpatient hospital settings.code_format:
0-9 and letters A-H, J-N, P-Z are used (O and I are omitted to avoid confusion).0FB03ZX (Excision of liver, percutaneous approach, diagnostic).notes: Used primarily by facilities for inpatient claims, not by physicians for professional fees (physicians use CPT).code_category: service / proceduredescription: Codes medical, surgical, and diagnostic services performed by physicians and other qualified healthcare professionals. Used for professional billing. Also known as HCPCS Level I.code_format:
99213 (Office outpatient visit, established patient, 15-29 minutes).notes: Maintained by the American Medical Association (AMA). Often used with modifiers (2 alphanumeric characters) to provide additional information (e.g., laterality -RT, -LT).code_category: service / product / supplydescription: Codes products, supplies, drugs administered other than orally, and services not directly covered by CPT (e.g., ambulance, durable medical equipment).code_format:
A-V), followed by 4 numeric digits.J0171 (Injection, adalimumab, 20 mg), E0601 (Continuous positive airway pressure (CPAP) device).notes: Maintained by CMS. Also uses modifiers (alphanumeric) similar to CPT, some specific to HCPCS Level II.code_category: payment_grouper / rate_codedescription: Used in specific prospective payment systems (PPS) to determine payment rates, particularly for Skilled Nursing Facilities (SNF under PDPM), Home Health (HHA under PDGM), and Inpatient Rehabilitation Facilities (IRF). Represents a case-mix group.code_format:
notes: Derived from patient assessment data (e.g., MDS for SNF, OASIS for HHA). Represents payment grouping, not a specific diagnosis or service itself.code_category: billing_detail / ancillarydescription: Used on institutional claims (UB-04 form) to summarize charges by department or cost center (e.g., room charges, pharmacy, laboratory, operating room). Groups line items for billing.code_format:
0300 (Laboratory), 0120 (Room & Board - Semi-Private - 2 Beds).notes: Maintained by the National Uniform Billing Committee (NUBC). Used by facilities (hospitals, SNFs, etc.).code_category: billing_grouper / payment_grouperdescription: A classification system that groups hospital inpatient cases into clinically coherent groups expected to consume similar hospital resources. Used primarily by Medicare (and some other payers) for inpatient facility payment.code_format:
291 (Heart Failure & Shock w MCC - Major Complication/Comorbidity).notes: Assignment is based on principal diagnosis, secondary diagnoses (including complications/comorbidities - CC/MCC), procedures performed, age, sex, and discharge status.code_category: billing_grouper / payment_grouperdescription: A classification system for grouping hospital outpatient services and procedures that are clinically similar and require comparable resources, for payment purposes under the Medicare Outpatient Prospective Payment System (OPPS).code_format:
5012 (Clinic Visit). Note: A single encounter can map to multiple APCs.notes: Payment is based on the APC assigned to the CPT/HCPCS codes reported on the claim. Multiple APCs can be assigned per encounter.code_category: billing_grouper / payment_grouperdescription: An alternative/enhancement to APCs used by some state Medicaid programs and commercial payers for grouping outpatient services (including clinic, emergency department, ambulatory surgery) based on clinical characteristics and resource use for payment.code_format:
notes: Aims to provide more granularity than APCs, often incorporating factors like diagnosis. Can bundle multiple services into one group (e.g., a visit EAPG plus a procedure EAPG might be assigned). Developed by 3M.code_category: billing_grouper / payment_grouperdescription: An inpatient classification system similar to MS-DRG but designed for all patient types (not just Medicare). It explicitly incorporates severity of illness (SOI) and risk of mortality (ROM) subclasses for each base DRG.code_format:
1-4) indicating SOI and ROM levels.XXX-S-R (e.g., 194-2-1 for Heart Failure, SOI 2, ROM 1). The base number (194) is the core group.notes: Developed by 3M. Considered by some to be more clinically nuanced than MS-DRG due to the explicit SOI/ROM subclasses. Used by many non-Medicare payers and for hospital quality/performance analysis.