ICD-10-CM

Key facts

Maintained by

CDC National Center for Health Statistics (NCHS)

HIPAA compliance date

October 1, 2015, replacing ICD-9-CM

Format

3 to 7 characters; letter first, decimal point after the third character

Update cycle

Annual release effective October 1, with possible April 1 updates

Size

More than 70,000 codes

What is ICD-10-CM?

ICD-10-CM stands for International Classification of Diseases, Tenth Revision, Clinical Modification. The World Health Organization (WHO) publishes ICD-10 for international statistics, and the National Center for Health Statistics (NCHS) at the Centers for Disease Control and Prevention (CDC) adapts it with far more clinical detail for U.S. use.

Under the Health Insurance Portability and Accountability Act (HIPAA), ICD-10-CM is the required diagnosis code set in standard transactions, in inpatient, outpatient and physician settings alike. It replaced ICD-9-CM on October 1, 2015. Procedures are coded separately: ICD-10-PCS for hospital inpatient procedures, and CPT or HCPCS elsewhere.

How ICD-10-CM codes are structured

Codes are 3 to 7 characters long and are organized into chapters by body system or type of condition. A decimal point follows the first three characters:

A code is valid for billing only at its most specific available level. The ICD-10-CM Official Guidelines for Coding and Reporting, approved by CMS and NCHS together with the American Hospital Association and the American Health Information Management Association, set the rules for selecting and sequencing codes.

• Characters 1 to 3: the category, such as E11 for type 2 diabetes mellitus.
• Characters 4 to 6: etiology, anatomic site, severity or other clinical detail.
• Character 7: an extension used in some chapters, such as A, D or S for initial, subsequent or sequela encounters for injuries.
• Placeholder X: fills empty positions so that a 7th character can be added.

Why ICD-10-CM matters

Diagnosis codes define who a patient is in most claims-based analysis:

• Patient cohorts in claims and EHR data are usually defined by lists of diagnosis codes, for example to size a disease population or find treating physicians.
• Medicare Advantage risk adjustment maps diagnoses to Hierarchical Condition Categories (HCCs), which affect plan payments.
• Inpatient diagnoses drive Medicare Severity Diagnosis Related Group (MS-DRG) assignment and hospital payment.
• Coverage policies, such as Medicare local coverage determinations, list the diagnosis codes that support medical necessity for a test or procedure.

ICD-10-CM vs ICD-10 and ICD-11

ICD-10-CM is not the same as WHO ICD-10. It adds many codes and characters that the international version lacks, so codes do not always match one to one. U.S. death certificates are coded with WHO ICD-10, not ICD-10-CM.

WHO ICD-11 took effect internationally in January 2022, but the United States has not adopted it for diagnosis coding. Any U.S. transition would require federal rulemaking.