International Classification of Diseases (ICD)

The International Classification of Diseases (ICD) is the result of close collaboration among many nations and nongovernmental organizations, under the auspices of the World Health Organization. Its original use was to classify causes of mortality; now the ICD has become the international standard diagnostic classification for all general epidemiology and many health management purposes.

The ninth revision of the ICD (ICD-9) was used to classify deaths beginning January 1, 1979, through December 31, 1998. Beginning January 1, 1999, deaths were classified using the tenth revision (ICD-10). This change affected the numbers of deaths attributed to some causes. Most striking are a decrease of about 30 percent in “Pneumonia and Influenza” deaths, an increase of 55 percent or more in deaths attributed to Alzheimer’s disease, and an increase of 23 percent or more in deaths attributed to “nephritis, nephrotic syndrome and nephrosis.”

For more information on these estimates and how the National Center for Health Statistics (NCHS) calculated them, see “Comparability of Cause of Death Between ICD-9 and ICD-10: Preliminary Estimates” at http://www.cdc.gov/nchs/data/nvsr/nvsr49/nvsr49_02.pdf .