ICD-9 Codes - Their History And Use In Medical Billing

Medical billers and coders use ICD-9 codes to describe patient diagnosis. Learn more about these medical billing codes here...

ICD-9 codes are an essential part of the medical billing and coding process. They describe the patient's diagnosis, or why the patient was seen by the healthcare provider.

From dental cavities to motor vehicle accidents to ear infections, all diagnoses are in the ICD-9 system.

As a medical billing specialist you will become very familiar with ICD-9 codes. It is likely you'll have an entire course devoted to ICD-9 as part of your medical billing school training.


ICD-9 stands for International Classification of Diseases, 9th Edition.

The use of a diagnosis coding system became a requirement through Medicare in the 1980s as a means of processing the large and often complex volume of claims submitted to the federal government.

Shortly after Medicare began requiring use of the system, most commercial insurance providers followed as a means of streamlining overall billing.

There have been different sets of ICD codes, and the current set is the ICD-9 code set. The "9" stands for "9th Edition."

The US Department of Health and Human Services is currently developing a new set of ICD codes, which more accurately reflect today's medical climate. This is the ICD-10 system, and comes into effect in 2013. It's likely that you will learn these new codes in your medical billing and coding classes.

This special coding system makes claims reporting quicker and easier. It is recognized by all parties in the medical field, and ICD-9 codes are used by medical practitioners, laboratories, insurance companies, and specialists.

See more on the history of medical coding here.

Use of Codes

Medical professionals use ICD-9 codes every day

ICD-9 codes are made up of a variation of numbers and letters.

The first three numbers are the most important, as they describe the area of the body or type of treatment. For instance, a common three digit ICD-9 code is 462, or pharyngitis (sore throat).

In many cases, there are one or two other numbers, following a decimal point after the first three. For example, a common five digit ICD-9 code is 786.07, or Reactive Airway Disease (wheezing). More specific codes have more numbers after the decimal point.

Other ICD-9 codes begin with a number, which indicate the reason for the patient's visit or gives more information about the diagnosis.

On claims, ICD-9 codes are always associated with CPT codes, which are the procedure codes.

The procedure and the diagnosis codes combined tell the story of what happened at the visit.

Example: if the diagnosis code indicates an ear infection, and the procedure code indicates an office visit, we can assume that the patient came into the office with an ear infection, was seen by the doctor at a regular sick visit.

Depending on the patient's diagnosis and the severity of the symptoms, the claim form may include many different diagnoses or procedure codes.

Sometimes there are a lot of diagnoses and only one or two procedures, but other times there are a lot of procedures and only one diagnosis. It all depends on the patient and what was done on the date of service.

List of Codes

The listing below will show you which numbers correspond to which areas of the body and types of treatment:

Doctors working 001-139: infectious and parasitic diseases
140-239: neoplasms
240-279: endocrine, nutritional and metabolic diseases, and immunity disorders
280-289: diseases of the blood and blood-forming organs
290-319: mental disorders
320-359: diseases of the nervous system
360-389: diseases of the sense organs
390-459: diseases of the circulatory system
460-519: diseases of the respiratory system
520-579: diseases of the digestive system
580-629: diseases of the genitourinary system
630-679: complications of pregnancy, childbirth, and the puerperium
680-709: diseases of the skin and subcutaneous tissue
710-739: diseases of the musculoskeletal system and connective tissue
740-759: congenital anomalies
760-779: certain conditions originating in the perinatal period
780-799: symptoms, signs, and ill-defined conditions
800-999: injury and poisoning
E and V codes: external causes of injury and supplemental classification

These codes are updated regularly through the main medical coding books. To learn more about medical codes, have a look at the history of medical coding.

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