ICD-9-CM (International Classification of Diseases, Ninth Revision, Clinical Modification)

The International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) is the U.S. health system's adaptation of international ICD-9 standard list of six-character alphanumeric codes to describe diagnoses. Standardizing codes improves consistency among physicians in recording patient symptoms and diagnoses for the purposes of payer claims reimbursement and clinical research.

ICD-9-CM contains a list of codes corresponding to diagnoses and procedures recorded in conjunction with hospital care in the United States. These codes may be entered onto a patient's electronic health record and used for diagnostic, billing and reporting purposes. Related information also classified and codified in the system includes symptoms, patient complaints, causes of injury, and mental disorders.

The United States Department of Health & Human Services and the Centers for Medicare and Medicaid Services (CMS) created ICD-9-CM as an extension of the Ninth Revision, International Classification of Diseases (ICD-9), which the World Health Organization (WHO) established to track mortality statistics across the world.

ICD-9, ratified in 1975 at a WHO conference, is the lingua franca upon which a majority of the U.S. healthcare payments system is based. Other code sets such as diagnosis-related groups and specialty-specific languages compose the balance. It is stable, and many standards and practices have developed around it. However, most other countries moved to the more granular and therefore more data-rich ICD-10 when it was released in the 1990s, leaving the U.S. behind as far as research capabilities are concerned.

In 2008, CMS announced it would adopt ICD-10-CM, the U.S. version of the ICD-10 update. Commercial insurers typically follow CMS's lead when it comes to standardized disease coding, and follow suit, making it a de facto national standard. However, due to technical and political issues surrounding the adoption of ICD-10-CM, its implementation has been put off numerous times. Some of the reasons physicians and hospitals cling to ICD-9 include its less rigorous clinical documentation than ICD-10 and its ability to justify common patient care episodes with general codes; its implementation timing coincides with other major U.S. health IT initiatives including nationwide EHR adoption, establishing national health information exchanges and data-intensive accountable care organizations. Upgrading from ICD-9 to ICD-10 will result in significant workflow changes that require physicians to create more up-front patient care documentation that is fully reimbursed at the claims stage weeks or months later.

Presently ICD-10 is scheduled to go live Oct. 1, 2015, after Congress stepped in and ordered CMS to delay its implementation. It is possible that some sectors of U.S. healthcare such as small employer-based payers, long-term care facilities, nursing homes and prison medical systems may never convert to ICD-10-CM, rendering U.S. healthcare a hybrid ICD-9/ICD-10 system for years to come.

In 2017, ICD-11 is scheduled to be released by WHO, the first ICD set whose development was digitally crowdsourced. While the idea doesn't have deep support among U.S. policymakers, the American Medical Association and other large organizations have suggested that replacing ICD-9-CM with ICD-11 and skipping ICD-10 altogether merits more research.

This was last updated in December 2014

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