Patient's Guide to Medical Codes

Medical codes are used to describe diagnoses and treatments, determine costs, and reimbursements, and relate one disease or drug to another.

Patients can use medical codes to learn more about their diagnosis, the services their practitioner has provided, figure out how much their providers were paid, or even to double-check their billing from either their providers or their insurance or payer. Learn more about these medical coding systems.

CPT Codes

A doctor writes in a medical chart

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Current Procedural Terminology (CPT) codes are developed by the American Medical Association to describe every type of service (i.e., tests, surgeries, evaluations, and any other medical procedures) a healthcare provider provides to a patient. They are submitted to insurance, Medicare, or other payers for reimbursement purposes.

Patients may be interested in looking at CPT codes to better understand the services their doctor provided, to double-check their bills, or negotiate lower pricing for their healthcare services.


Healthcare Common Procedure Coding System (HCPCS) codes are used by Medicare and are based on CPT codes. Patients who use Medicare, especially those who have needed ambulance services or other devices outside of the doctor's office, may want to learn more about HCPCS codes.

There are two levels:

  • Level I HCPCS codes mirror CPT codes and are used to identify medical services and procedures ordered by physicians or other licensed professionals.
  • Level II HCPCS codes are alphanumeric and identify non-physician services like ambulance rides, wheelchairs, walkers, other durable medical equipment, and other medical services that don’t fit readily into Level I.

ICD Codes

International Classification of Diseases (ICD) is published by the World Health Organization (WHO). This diagnostic classification system is the international standard for reporting diseases and health conditions. It uses death certificates and hospital records to count deaths, as well as injuries and symptoms.

ICD codes change over time, so they have a number appended to them to show which set of codes is being used. Introduced in the late 1970s, the ICD-9 code set was replaced by the more detailed ICD-10 code set on October 1, 2015. 

ICF Codes

The International Classification of Functioning, Disability, and Health, commonly known as ICF, is a framework for measuring health and disability related to a health condition. Where the ICD classifies disease, the ICF looks at how functional a person is in their environment.

DRG Codes

The diagnostic-related group (DRG) system categorizes different medical codes. Hospital services are categorized based on a diagnosis, type of treatment, and other criteria for billing purposes.

This means that hospitals are paid a fixed rate for inpatient services corresponding to the DRG assigned to a given patient, regardless of what the real cost of the hospital stay was, or what the hospital bills the insurance company (or Medicare) for.

The assumption is made that patients that fit the same profile will need approximately the same care and services. There are about 500 different DRGs. They are updated annually to add new diagnoses or circumstances.

NDC Codes

The National Drug Code (NDC), is a unique, numeric identifier given to medications. The code is present on all nonprescription (OTC) and prescription medication packages and inserts in the US. The NDC is 10-digits divided into three segments:

  • The first segment identifies the product labeler (manufacturer, marketer, repackager, or distributor of the product).
  • The second segment identifies the product itself (drug-specific strength, dosage form, and formulation).
  • The third segment identifies the package size and type.

It should be noted that just because the number is assigned, that does not mean the drug has been approved by the FDA. The FDA publishes a list of NDC codes in the NDC Directory which is updated daily.

CDT Codes

Code on Dental Procedures and Nomenclature (CDT) codes allow dentists to get into the coding act. It is a set of procedural codes for oral health and related services.


Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR) codes are used to diagnose psychiatric illnesses. They are published and maintained by the American Psychiatric Association.

While you may see these codes in existing patient records, the fifth edition of the DSM was published in 2013 and recommends ICD-10 codes for psychiatric conditions. These also change over time, as there was a revision in October​ 2017.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Medical Association. CPT (Current Procedural Terminology).

  2. Centers for Medicare & Medicaid Services. HCPCS - General Information.

  3. Centers for Medicare and Medicaid Services. ICD-10.

  4. World Health Organization. International Classification of Functioning, Disability and Health (ICF). Geneva: World Health Organization.

  5. Hospital acute inpatient services payment system.

  6. U.S. Food and Drug Administration. National Drug Code Directory.

  7. CDT: Dental Procedure Codes. American Dental Association.

  8. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR). American Psychiatric Association.

  9. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Arlington, VA: American Psychiatric Association.

By Trisha Torrey
 Trisha Torrey is a patient empowerment and advocacy consultant. She has written several books about patient advocacy and how to best navigate the healthcare system.