What is the difference between ICD-9 and ICD-10?

In many ways, ICD-10-CM is quite similar to ICD-9-CM. The guidelines, conventions, and rules are very similar. The organization of the codes is also very similar. Anyone who is qualified to code ICD-9-CM should be able to easily make the transition to coding ICD-10-CM.

Many improvements have been made to coding in ICD-10-CM. For example, a single code can be found to report a disease and its current manifestation (i.e. type II diabetes with diabetic retinopathy). In fracture care, the code differentiates between an encounter for an initial fracture, follow-up for a fracture that is healing normally, follow-up for a fracture in malunion or nonunion, and follow-up for late effects of a fracture. Likewise, the trimester is designated in obstetrical codes.

While much has been said about the huge increase in the number of codes under ICD-10-CM, some of this growth is due to laterality. For example, while an ICD-9-CM code may identify a condition of the ovary, the parallel ICD-10-CM code identifies four codes: unspecified ovary, right ovary, left ovary, or bilateral condition of the ovaries.

 The big differences between the two systems are differences that will affect information technology and software.

No. & Type of Digits
ICD-9 codes consist of 3-5 digits:
• Chapters 1-7 are numeric
• Supplemental chapters: the first digit is alpha (E or V) and the rest are numeric

ICD-10-CM codes consist of 3-7 alphanumeric characters:
• Digit 1 is alpha
• Digit 2 is numeric
• Digits 3-7 are alpha or numeric

ICD-10-PCS codes consist of 7 alphanumeric characters:
• Each digit can be alpha or numeric
• Numbers used are 0-9
• Alpha letters I and O are not used in order to eliminate confusion

Volume of Codes
2009 totals, according to the U.S. Department of Health and Human Services:
ICD-9-CM: 17,000
Diagnosis: 13,000
Procedure: 4,000

ICD-10: 140,694
Diagnosis (ICD-10-CM): 68,105
Procedure (ICD-10-PCS): 72,589

Format & Structure
The format and structure of the ICD-10 codes varies greatly from the previous diagnosis codes. The ICD-10-CM is divided into an index. The first is the alphabetical list of terms and their corresponding code. The second is the Tabular List, a chronological list of codes divided into chapters that represent different conditions or body systems. There are also two parts to the Index – the Index to External Causes of Injury and the Index for Diseases and Injury. The Index and Tabular portions of the ICD-10-CM include the conventions and structural notes.

The Tabular List contains alphanumeric categories, subcategories, and codes. When a three character category has no more subdivisions, it is considered a code. Each level of subdivision after the category is a subcategory. The ‘code’ is considered complete once there are no more subcategories. A code indicated to have a 7th character is considered incomplete without the missing character.

In order to be reportable, only a complete ‘code’ can be used. Subcategories or diagnoses that are not complete cannot be used for reporting. When there is an unknown subcategory, the place holder X is allowable in either the 5th or 6th position. This placeholder allows for the future addition of characters, thereby accommodating expansion when needed. The notes in the Tabular List will indicate categories where a 7th character is required.

The abbreviations NEC and NOS are still used in both the Index and Tabular sections. When used in a narrative statement, the word “and” is defined as “and/or.” To locate a code and its classification, first refer to the Tabular List. The Index does not always provide the full code and therefore it is necessary to review both the Index and the Tabular List.