ICD coding system

ICD coding system

ICD (International Classification of Disease) is a coding system for which the first edition was published in 1900, and it is being revised at approximately 10-year intervals. The most recent version is ICD-10, which was published in 1992. WHO is responsible for its maintenance.

In US, the coding is still based on ICD-9-CM, which contains more detailed codes.
ICD consists of a core classification of three-digit codes, which are the minimum requirement for reporting the reason for the encounter. An optional fourth digit provides an additional level of detail. At all levels, the numbers 0 to 7 are used for further detail, whereas the number 8 is reserved for all other cases and the number 9 is reserved for unspecified coding.

The basic ICD is meant to be used for coding diagnostic terms, but ICD-9 as well as ICD-10 also contains a set of expansions for other families of medical terms. For instance, ICD-9also contains a list of codes starting with the letter “V” for reasons for encounter or other factors that are related to someone’s health status. A list of codes starting with the letter “E” is used to code external causes of death. The nomenclature of the morphology of neoplasms is coded by the “M” list.
The disease codes of both ICD-9 and ICD-10 are grouped into chapters. For example, in ICD-9, infectious and parasitic diseases are coded with the three-digit codes 001 to 139, and in ICD-10 the codes are renumbered and extended as codes starting with the letters A or B; for tuberculosis the three-digit codes 010 to 018 are used in ICD-9, and the codes A16 to A19 are used in ICD-10. The four-digit levels and optional five-digit levels enable the encoder to provide more detail. Table below gives examples of some codes in the ICD-9 system.

Example of a Four-Digit Code Level in ICD-9 and the Five-Digit Code Level as Extended by the ICD-9-CM
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Code Disease
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001 - 139 Infectious and parasitic diseases
001 - 009 Infectious diseases of the digestive tract
003 Other Salmonella Infections
- 003.0 Salmonella gastroenteritis
- 003.1 Salmonella Septicemia
- 003.2 Localized Salmonella Infections
- 003.20 Localized Salmonella Infection, Unspecified
- 003.21 Salmonella Meningitis
- 003.22 Salmonella Pneumonia
- 003.23 Salmonella Arthritis
- 003.24 Salmonella Osteomyelitis
- 003.29 Other Localized Salmonella Infections
- 003.8 Other Specified Salmonella Infections
- 003.9 Salmonella Infections, Unspecified
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The U.S. National Center for Health Statistics published a set of clinical modifications to ICD-9, known as ICD-9-CM. It is fully compatible with ICD-9, but it contains an extra level of detail where needed. In addition, ICD-9-CM contains a volume III on medical procedures.