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What are ICD-9 or ICD-10 Codes?

How ICD Codes Affect Your Care

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Updated April 15, 2014

ICD means International Statistical Classifications of Diseases. ICD codes are alphanumeric designations given to every diagnosis, description of symptoms and cause of death attributed to human beings.

These classifications are developed, monitored and copyrighted by the World Health Organization (WHO). In the United States, the NCHS (National Center for Health Statistics), part of CMS (Centers for Medicare and Medicaid Services) oversees all changes and modifications to the ICD codes, in cooperation with WHO.

Here is how WHO describes the ICD system: ICDs apply to "all general epidemiological, many health management purposes and clinical use. These include the analysis of the general health situation of population groups and monitoring of the incidence and prevalence of diseases and other health problems in relation to other variables such as the characteristics and circumstances of the individuals affected, reimbursement, resource allocation, quality and guidelines."

What does that mean to us patients? It means that each diagnosis a human being may be given has a code, a numbered designation, that goes with it. That code means that every medical professional in the United States and many other parts of the world will understand the diagnosis the same way. So, for example, if I am diagnosed with GERD (acid reflux), it will be given the code 530.81. If I travel across the country and need to see a doctor for my heartburn, he will also put a 530.81 on my record. The 530.81 is the ICD classification.

If the diagnosis is for something acute, something that goes away with treatment like a rash or the flu, then the ICD code will be less important to us. Because the illness or condition will go away, the code will stay on our record, but won't affect future care. However, if we are diagnosed with a chronic or lifelong problem, like heart disease or diabetes, then the ICD code will follow us for most of our medical care, and will help our healthcare providers make determinations about our care. As electronic medical records are implemented across the country, these codes will affect our care more and more.

(Learn how to look up your own ICD code.)

There Are Several ICD Code Sets

There are actually several lists of these codes, all of which relate to each other. While the code numbers may be the same, sometimes they will have extra numbers or letters attached to them for different uses. In these examples, the use of # will relate to a number. See a description for these numbers, below.

  • ICD-##-CM codes are used for diagnosis purposes. CM means "clinical modification." It is used by hospitals and other facilities to describe any health challenges a patient has, from his diagnosis to symptoms to outcomes from treatment, to causes of death. As we move more and more into electronic medical records, these codes will be used even further by physicians and other medical professionals.

  • ICD codes are used by government health authorities to track certain diseases. For example, if someone contracts the flu, an ICD-9-CM 486 will be recorded. Certain diseases, often those that are highly contagious, or those that have public health interest like lung cancer or HIV, are tracked by authorities to help ascertain how they spread, where they are prevalent, and perhaps to help budget programs or research to work on prevention.

  • ICD codes are also used to describe a cause of death. They are added to death certificates to explain why someone has died. Many of these, too, are tracked by health authorities.

  • ICD codes are used internationally (remember, they emanate from WHO) and each country may tailor the codes to fit their own needs. Therefore, some code sets will have extra letters addended to them to describe which country they come from. For example, ICD-##-CA codes are used in Canada and ICD-##-AM codes are used in Australia.

What Do the Numbers Mean? ICD-09, ICD-10 and Others

ICD codes were first developed in 1893 in France by a physician, Jacques Bertillion. They were called the Bertillon Classification of Causes of Death. In 1898, they were adopted in the United States, and were considered, in effect, ICD-1 because that was the first version of code numbers.

Since then, as medical science has progressed and new diagnoses have been developed, named and described, the code lists have been updated. The number designation changes when the updates are so extensive that a wholesale change needs to be made. There may be annual updates, too, but those are considered to be relatively minor, and the basic code set doesn't change. For example, the upgrade in 1949, ICD-6, was the first time mental disorders were added to the code set. The upgrade in 1977 to ICD-9 was the first time procedure codes were added, and the CM designation was included.

Most of the codes we see in the United States today are version 9, called ICD-9-CM codes. With few exceptions, the paperwork we receive when we leave a doctors office will contain both CPT codes (Current Procedural Terminology) to describe the service that was rendered for billing purposes, and ICD-9-CM codes to describe why that service was provided. Further, most death certificates filed since 1977 will have an ICD-9 code on them.

The most current list of codes in use is ICD-10 which is beginning to be implemented in the United States. This list was first used in the United States in 2007. Minor revisions added to ICD-10 codes were made available in early 2009 by the National Center for Health Statistics. Globally, most other countries in the world have implemented the ICD-10 codes. There are some major differences between the ICD-9 and ICD-10 code sets, the transition is very expensive, and most American providers have not yet upgraded to the ICD-10 system.

ICD-11, the next major update, is in development but does not have a designated implementation date.

If you see ICD codes on your medical paperwork, like doctor's service receipts, doctors' bills or your EOB (explanation of benefits) from your payer, you may want to match the ICD code to your diagnosis.

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