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What Is the Definition of an ICD-9 Code?

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The ICD-9 is an acronym for "International Statistical Classification of Diseases and Related Health Problems 9th Revision." This ninth edition is a publication from the World Health Organization comprising a set of codes that are used worldwide to classify diseases and injuries.


Medical facilities use ICD-9 codes any time they receive patients. When physicians make their diagnoses, medical coders and billers assign the appropriate code. In the United States, the ICD-9 code is used with the Current Procedural Terminology (CPT) code, which is for procedures performed in the facility. These codes are used to generate bills for facility reimbursement in cases where patients have health insurance.


The ICD can be traced as far back as 1893, when a French doctor named Jacques Bertillon introduced the Bertillon Classification of Causes of Death at the International Statistical Institute in Chicago. Within five years, a handful of countries--including the United States, Canada and Mexico--had adopted it. The WHO assumed responsibility for developing and publishing revisions of the system every 10 years, starting in 1948, and it received its official name in 1959. The ICD-9 arrived in 1977.

ICD-9 Classifications

The ICD-9 is split into several sections that correspond to a type of disease or injury. Each section is assigned to a range of numbers, each of which denote a medical condition. For instance, codes 320 to 359 are categorized as diseases of the nervous system, and this section contains medical conditions such as Parkinson's disease (331) and multiple sclerosis (340). In many cases, these medical conditions are split into more specific afflictions. For instance, hemiplegia (342) is divided into the flaccid (342.0) and spastic kinds (342.1).


The National Center for Health Statistics--a division of the Centers for Disease Control and Prevention (CDC)--wanted to expand the ICD-9 for additional data on the rate of incidence of diseases (morbidity). Thus, the ICD-9-CM was introduced. It consists of three volumes: Volume 1 is a tabular listing of the diagnosis codes, Volume 2 is its index and Volume 3 comprises procedure codes. The ICD-9-CM is updated yearly on Oct. 1.

Current Status

As of June 2010, the WHO no longer publishes or distributes ICD-9 codes, and they are now public domain. The United States continues to use the ICD-9-CM. As of Oct. 1, 2013, however, medical facilities throughout the nation will begin using its successor, the ICD-10.


Based in the D.C. area, Andy Joseph works full-time as a data analyst and technical writer. He has been writing articles about technology, health, politics, music, culture and automobiles since 2007. His work has appeared in The Express, Congressional Report and Road & Track. He has a master's degree in journalism and technology management.