Medical Diagnostic Codes

A description of what Medical Diagnostic Codes are and how they are used. Explanation of the ICD 9 Medical Insurance Code and the ICD 10 Medical Insurance Codes.

The diagnostic codes used in medical billing and coding are used by health care providers to document the disease or condition using a standard classification. The International Classification of Diseases (ICD) is a system of medical diagnostic or medical insurance codes that were developed by the World Health Organization (WHO).

For several years, the standard medical diagnostic code system used to classify medical diseases and conditions has been the ICD-9. The WHO no longer maintains the ICD-9 codes as they are considered public domain. There are limitations to the 5 digit ICD 9 codes which limits classifications available. This has lead to the development and adoption of ICD 10 medical diagnostic codes with 7 alpha or numeric digits.

The ICD codes are not only used as medical insurance codes, but to identify and track health care trends and disease threats. It also provides a means of evaluating the use of new procedures and technologies used. Since the ICD-10 system is used by most other countries, it’s important when tracking and responding to emerging diseases that U. S. data comparisons are compatible with other international health care data. This has been evident in the last decade as diseases emerge in one country and spread quickly to other countries.

ICD-9 Codes
ICD-9 codes manual (or ICD-9-CM) consists of 17 chapters as listed here. The CM stands for Clinical Modification. These medical diagnosis codes are used for diagnoses associated with inpatient, outpatient, and physician office visits. The ICD-9-CM was created by the National Center for Health Statistics (NCHS) and is updated yearly is based on the ICD-9 but provides for additional morbidity detail and is annually updated. Any changes are administered by the NCHS and the Centers for Medicare and Medicaid Services.

ICD-9-CM consists of three volumes. Volumes 1 and 2 are the medical insurance diagnostic codes, volume 1 is a table listing, and volume 2 is an indexed listing. Volume 3 is a tabular list of procedures used by hospitals for coding inpatient procedures.

ICD-9-CM also includes supplementary classifications; V codes and E codes. V codes categorize health status and contact with health services when a patient experiences something other than an injury or disease. When there are external causes of injury, the E code medical diagnostic code is used to classify the injury. E code medical diagnostic codes would be used for accidents, poisoning, criminal injuries, or other injuries sustained by an environmental event.

The four appendices to the ICD-9-CM medical insurance diagnostic codes are:

  • Appendix A: Morphology of Neoplasms
  • Appendix C: Classification of Drugs by the American Hospital Formulary service
  • Appendix D: Classification of Industrial Accidents by Agency
  • Appendix E: List of three digit categories

ICD 10 Codes – The Future of Diagnosis Codes
ICD 10 codes consist of 22 chapters listed here. The “10” identifies these medical diagnostic codes as being the 10th revision. The largest benefit of the ICD 10 classifications is that it will allow 155,000 different codes compared to only 17,000 for ICD 9. The E and V code supplementary classifications in ICD-9-CM are now incorporated in ICD-10 classification system.

While many other countries have already adopted ICD-10 diagnosis classification, the United States has not yet. The transition to ICD-10-CM codes will be led by Medicare and Medicaid. The US Department of Health and Human Services proposed the ICD-9-CM code sets be replaced by ICD-10 effective October 1, 2013.

The ICD-10-CM medical diagnostic codes will replace volumes 1 and 2 of ICD-9-CM. The ICD-10-PCS is intended to replace volume 3 of the ICD 9 codes.

Differences and Similarities Between ICD-9-CM and ICD-10-CM Codes

  • 3 to 5 characters
  • First character can be numeric or alpha (E or V)
  • Following characters 2 thru 5 are numeric
  • Minimum 3 characters
  • Decimal after 3rd character


  • 3 to 7 characters
  • First character alpha
  • Following characters 2 thru 7 can be numeric or alpha
  • Minimum 3 characters
  • Decimal after 3rd character

Transition to ICD-10
ICD-10-CM does not have a dramatically different organization than the ICD-9-CM medical diagnosis codes it replaces. The benefit is the additional detail and number of codes provided by ICD-10. The American Health Information Management Association (AHIMA) estimates that most medical coding professionals will require 16 hours of training to learn the new ICD-10-CM coding system. It’s important to remember that most providers only use a small number of the same medical insurance codes so 16 hours sounds like a worst case training commitment. Most providers offices will probably take more of a “learn as you go” approach to becoming familiar with the new coding system. However this transition does have the potential to be very disruptive to the reimbursement of a practice if not prepared for.

The Future: ICD-11
There are other potential changes down the road for medical diagnosis codes. The World Health Organization is preparing a draft of revision 11 of the medical diagnostic codes. Publication of the ICD-11 classification system is expected in 2014 after the first draft is published in 2010. Implementation is expected around 2015 or later. The WHO allows suggestions for input for those willing to participate and document their suggestions.

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