The History of Medical Coding

In the United States, the history of medical coding primarily concerns ICD (International Classification of Diseases) Diagnosis codes, CPT (Current Procedural Terminology) treatment codes, and the HCPCS (Healthcare Common Procedure Coding System) coding systems.

History of Medical Coding - Diagnosis (ICD)

The origins of disease classification dates back to the 1600’s when when John Graunt began a system to classify mortality rates in England. This study became know as the London Bills of Mortality. It was established to determine the proportion of children who died before the age of 6.

In the mid 1800’s William Farr, a medical statistician, began to classify diseases for the General Register Office of England and Wales. Farr attempted to establish a better classification and uniformity of diseases resulted in an effort to arrange them into five groups: epidemic, general, local according to anatomical site, developmental, and those due to violence.

In 1885, the Bertillon committee in Paris met to adopt a classification system including English, German, and Swiss classifications and based on the principles proposed by Farr. It was called the Bertillon Classification of Causes of Death. This classification was the first to receive approval and adoption by several countries, including North America (Canada, United States, & Mexico).

The Bertillon effort evolved into the International List of Causes of Death by 1900. The classification was revised at 10 year intervals until 1920. The fourth revision occurred in 1929 followed by the fifth in 1938. The fifth revision approved three lists: detailed list of 200, intermediate list of 87, and an abridged list of 44 titles. These lists included updates of infectious and parasitic diseases and reflected the progress made in medical science.

Around this time the conference governing the revision, the Health Organization of the League of Nations, recognized the need for a list to meet the need of a variety of interests. This included insurors, health administrators, hospitals, and military medical providers. At this point the name of International Lists of Diseases was adopted.

The International Health Conference in 1946 had the International Commission of the World Health Organization (WHO) prepare the sixth revision of the International Lists of Diseases and Causes of Death. This sixth revision became known as the Manual of the International Statistical Classification of Diseases, Injuries, and Causes of Death. It consisted of two volumes with Volume 2 being an alphabetical index for diagnostic terms. This began a new era of internationally adopted lists overseen by the WHO.

The Seventh revision was approved in 1955. It incorporated essential changes along with amendments of errors and inconsistencies.

The Eighth revision was approved 10 years later in 1965 and was more substantial but did not change the basic structure and philosophy.

The Ninth revision followed in 1975 which is the ICD-9 codes used today. It added detail at the 4-digit subcategories with optional 5-digit subdivisions. It also included changes to increase the flexibility of the ICD for different situations.

A very detailed history of medical coding for the ICD classification system can be found from the World Health Organization site here.


The Tenth revision to the ICD approved in 1995 introduced a change in the structure of the classification system. ICD 10 codes are three to seven characters, the first is alphabetic, 2nd through 7th can be alphabetic or numeric with a decimal after 3 characters. Diagnosis codes are arranged in chapters and sub-chapters with diseases grouped by letter. This allows more detail and flexibility for emerging diagnosis. ICD-10 allows over 155,000 codes compared to a maximum of 17,000 ICD-9 codes.

The United States is scheduled to adopt ICD-10 in October 2014. Most of the international community has adopted ICD-10.

A system originally intended to classify the cause of death evolved into a system to track diseases and injuries. This evolved into the current ICD-9 diagnosis coding convention used today. It is key to providing a means of identifying patterns in diseases to identify epidemics and to track general health trends.

History of Medical Coding - Treatment Codes

HCPCS - Healthcare Common Procedure Coding System

The HCPCS coding system was developed in 1983 by the Centers for Medicare and Medicaid. it is also referred to as “Hick Picks”. The intent of HCPCS was to provide a standardized coding system for healthcare - both services and supplies. The HCPCS system is based on the American Medical Association’s (AMA) CPT codes.

The use of HCPCS became necessary for all government (Medicare & Medicaid) and private insurers to process claims consistently. It was adopted in 1983. It’s intent was to provide a uniform way to classify services, standardize coding, and meet the needs of Medicare and Medicaid.

HCPCS consists of three levels of codes:

  • Level I - American Medical Association CPT codes.
  • Level II - Codes for non-physician services not covered by CPT codes like ambulance, supplies, and medical devices. These codes begin with letters (A thru V) followed by four numeric digits. Level II codes are updated every year.
  • Level III - Local codes developed by Medicare contractors, and state Medicaid organizations, and private insurance companies. These codes have a similar structure to Level II codes and begin with the letter W thru Z and followed by four digits. Level III use was discontinued in 2003 in favor of coding that is consistent regardless of agency or location.

History of Medical Coding - CPT System

CPT stands for Current Procedural Technology. These are codes that identify the services performed on a patient by doctors and other healthcare providers. CPT codes were developed by the American Medical Association in 1966. The first addition of CPT codes was numeric with two to four digits. The original intent of CPT codes as not to be used for payment of insurance claims. It was intended as a simplified means for doctors to document procedures performed on patients for purpose of medical records.

The second edition of the CPT codes occurred in 1970. The procedure coding system developed into a 5 digit format.

In 1983 the Centers for Medicare and Medicaid Services (formerly Health Claim Financial Administration) combined the HCPCS coding system with the CPT coding system. The CPT coding system was to be maintained by the AMA and required its use for all Medicare billing.

New editions of the updated CPT codes are released each year in October. Codes are added, removed, and revised with each revision. Changes to codes can be initiated by providers, medical societies, or responsible organizations. Changes are governed by the CPT editorial panel consisting of 16 representatives.

HIPAA Impact on the History of Medical Coding

IN 1996, legislation called the Health Insurance Portability and Accountability Act (HIPAA) was enacted. HIPAA had provisions in the Administrative Simplification statue impacting coding. Called Transaction and Code Set Standards, this required the adoption of specific code sets for diagnosis and treatment codes. The HIPAA adopted HCPCS, CPT-4, CDT (Dental Codes), ICD-9, and NDC (National Drug Codes). HIPAA also required the use of unique identification numbers for providers and insurance companies. HIPAA mandated the use of ICD-10 diagnosis codes beginning October 1st, 2014.

History of Medical Coding Summary

So the history of medical coding can be traced back to England in the 1600's as a way of classifying death. This evolved through an international effort that resulted in the ICD-9 and ICD-10 diagnosis codes we use today.

CPT codes were more recently developed in the United States by the AMA in the 1960's as a shorthand way to document medial treatment. These later evolved and matured to be endorsed by the federal government and universally used for the reimbursement of insurance claims.

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