Medical coding is the process of translating information about patient diagnoses, procedures, equipment and services into standardized, universally accepted numeric or alphanumeric data. These codes consolidate information from various sources, like lab test results, physician notes and more.
Thousands of these codes exist across widely accepted sources that healthcare coding professionals draw from. The most widely used source is the World Health Organization (WHO) and its International Classification of Diseases (ICD). The current version is ICD-10-CM — the 10th edition, clinically modified — which contains over 70,000 codes.
Subsets also exist for specific services and healthcare providers, such as the ICD-10-PCS, which applies to hospital-based surgeries and procedures. Other sources for coding can include:
- Current Procedural Terminology (CPT®), developed by the American Medical Association and typically used for outpatient services.
- Code on Dental Procedures and Nomenclature (CDT®), established by the American Dental Association and used for oral procedures and dental work.
- Healthcare Procedural Coding System Level II (HCPCS Level II), designed for Blue Cross/Blue Shield, Medicaid and Medicare.
- National Drug Code (NDC), specifying any drugs sold, used or prescribed.
Medical coding can be difficult due to ever-evolving regulations and error-prone manual data entry. Plus, codes frequently change, which adds complexity to the task and reinforces the need to stay current. For example, the 2025 update to the CPT introduces 270 new codes, 112 deletions and 38 revisions. ICD-10-CM saw similar volumes, with over 300 changes.