Description of How the ICD-9 Is Organized

Although the ICD-9 coding system first came into use as a way of gathering statistics about diseases, injuries and causes of death, medical providers now use these numeric codes to bill insurance companies. The ICD-9, or International Classification of Diseases, 9th Revision, is organized into a three-volume set of books. Coders look up diagnosed conditions in the second volume first, which is arranges alphabetically. Then they look in Volume 1 for more detailed coding instructions.

Structure of ICD-9 Codes

• Complete ICD-9 codes are five digits long. The first three digits represent the category, or general description, of the disease, and are followed by a decimal point. The next digit after the decimal is the subcategory of that disease, and the fifth and final digit is a sub-classification that adds more detail. For example, 715 is the category, "osteoarthritis." "Localized primary osteoarthritis" is 715.1, and 715.14 is "Localized primary osteoarthritis of the hand."

Volume 1: Tabular List of Diseases and Injuries

• Volume 1 lists the codes for disease and injuries in tabular, or numerical order. It has 17 chapters, each of which contains a range of the three-digit categories. Each chapter covers a broad grouping of related diseases or of diseases that affect a particular body system. The chapters are further broken down into sections, which are smaller ranges of categories.

  Each three-digit category is listed along with its description in medical terminology. Coders find all of the codes and descriptions for the related subcategories and sub-classifications in the indented list under each category. Some categories include extra coding instructions that are not found in Volume 2.

  The appendixes in Volume 1 have additional information to help coders, such as descriptions of different forms of cancer or types of industrial accidents. There are also two sections of special alphanumeric codes: V-codes, which describe reasons for medical visits not directly related to a disease, such as check-ups; and E-codes, which provide extra information about causes of injury or poisoning.

Volume 2: Alphabetic Index of Diseases and Injuries

• The entries in Volume 2 are arranged alphabetically by the medical terms, with the codes following. The alphabetizing is letter-by-letter rather than word-by-word. Coders look up terms that are in doctors' reports or patients' charts in this volume first. It contains the same categories as Volume 1, listed in bold print, with the same subcategories indented below in regular type. But it is still necessary to verify the coding in Volume 1.

  Volume 2 also has alphabetical lists of the E-codes, one for chemicals and drugs that cause poisoning and one for causes of injury.

Volume 3: Tabular List and Alphabetic Index of Procedures

• Volume 3 is like a combination of Volumes 1 and 2, but for procedural codes instead of disease codes. These codes go into a separate space on hospital billing forms, and describe care given to inpatients of hospitals. They are four-digit codes, organized in the tabular section of the book according to the body system they involve. Medical coders use a different coding system for outpatient procedures in doctors' offices that is not part of the ICD-9.