Naming Conventions in ICD 10 Coding Systems


ICD-10 stands for International Classification of Disease, Tenth Edition. It is a coding system that was created in 1989 by the World Health Organization (WHO) to replace ICD-9. It is the foundation from which the U.S. ICD-10-CM (clinical modification) was built.

ICD-10 as written by WHO contains diagnosis codes exclusively. It has been adopted by nearly every country in the world, although some countries have created their own modifications. ICD-10 is already being used in the United States, but only for mortality reporting done for the CDC (cause of death). For now, U.S. diagnoses continue to be reported with ICD-9-CM.

ICD-10 has fewer codes and less specificity than our current ICD-9-CM, and therefore would be unacceptable as a U.S. code set without modification.

The designation “ICD-10” is often used to describe the concept of change when the speaker or writer is discussing the concurrent adoption of ICD-10-CM and ICD-10-PCS: note its use in the American Medical News headline quoted at the top of this page: CMS calls for transition to ICD-10 codes in 3 years. What the AMA’s shorthand intents to communicate is CMS calls for transition to ICD-10-CM and ICD-10-PCS codes in 3 years.

Although WHO’s ICD-10 is exclusively a diagnostic coding system, when “ICD-10” is used to describe the concept of change to both systems, it references ICD-10-CM, the diagnostic classification, and ICD-10-PCS, a procedural coding system specific to hospital reporting.
This means that although ICD-10 is an official WHO diagnosis coding system, “ICD-10” in the United States may be referring to the future U.S. diagnostic and procedural coding systems.


ICD-10-CM is the clinical modification of WHO’s diagnostic system for the United States. ICD-10-CM will replace ICD-9-CM on Oct 1, 2015. ICD-10-CM increases the number of diagnostic codes more than fivefold, and increases the potential number of digits within a code from five to seven. Alphabetic characters have been added to many ICD-10-CM codes, and the changes mean ICD-10-CM will significantly impact information technology, physician documentation, and coding productivity when implemented across all aspects of U.S. healthcare. In some instances, ICD-10-CM is referred to as simply ICD-10, icd10, or just I-10.


ICD-10-PCS is a procedural coding system developed for reporting hospital procedural services. After implementation of the new classifications, physicians will still report their services with CPT® codes. However, the hospitals who provide the operating rooms, nursing services, and hospital beds for patients will report patient procedures using ICD-10-PCS. Implementation of the PCS system is scheduled to coincide with implementation of the new diagnostic coding system.

ICD-10-PCS has no relationship with WHO, and carries in its title “ICD-10” because CMS wanted to link it to ICD-10-CM, since both coding systems are components of the MS-DRG system under which hospitals are paid for Medicare services. In some circles, the name of ICD-10-PCS is shortened to “PCS.”
