ICD-10: History and Context

Pre-ICD-10.

Some scholars track the origin of ICD to 1763. The French physician and botanist Dr François Bossier de Sauvages de Lacroix developed a categorization of 10 distinct classes of diseases, which were further divided into 2400 unique diseases.¹ Sauvages de Lacroix was a contemporary and friend of the Swedish naturalist Carl Von Linné, considered the father of modern taxonomy. His classification system, built on earlier work by the English physician Thomas Sydenham, was similar to methods used by botanists at the time. Recognizing the importance of disease classification, the first International Statistical Congress held in Brussels in 1853 appointed Jacob Marc d'Espine and William Farr to develop a system of classifying causes of mortality that could be used across borders and languages.² This was the genesis of what became known as the “International List of Causes of Death.” History will prove the sagacity of these early thought leaders. In 1893, Jacques Bertillon, a Parisian statistician, and his committee established the first “International List of Causes of Death.”³ At around that time, the “International List of Causes of Death” was presented in the United States at the International Statistical Institute, and in 1898, various countries in North America, including the United States, adopted this system.⁴ Across time, this “International List of Causes of Death” was updated and published about once per decade in 1900, 1910, 1920, 1929, and 1938.⁵

The many twists and turns taken by this process during the half-century described are beyond the intended scope of this article. Suffice it to say that challenges were raised to the development of a reporting system for morbidity. In 1948, the World Health Organization (WHO) took charge of the classification system, which was expanded the following year to include coding for causes of morbidity in addition to mortality. The system was rechristened the International Classification of Disease system.^2,4 Under the auspices of the WHO, ICD development continued in a more predictable manner. The first 5 versions of the ICD system were each entirely contained within a single volume. That volume included an alphabetic index and a tabular list. By the sixth revision, the coding system included morbidity and mortality designations and required 2 volumes. Most important, ICD-6 expanded to include a section on psychiatric disorders. This sixth version was now called the Manual of the International Statistical Classification of Diseases, Injuries, and Causes of Death (http://apps.who.int/iris/bitstream/10665/70934/2/ICD_10_1967_v1_eng.pdf). Revisions have continued on an approximately decade-by-decade basis under the WHO, and the seventh and eight revisions were published in 1957 and 1968.³

In what could be called a parallel effort, the United States Public Health Service adapted the ICD to index hospital records and classify surgical procedures (ICDA) and published this system in 1962. The seventh edition of the ICD, therefore, expanded to include materials thought to be necessary for categorizing needs for hospitals. The Public Health Service went on to publish an eighth revision of the ICD, specifically focused on the unique needs of the United States known as ICDA-8. It had additional focus on morbidity and mortality reporting.³

The ICD-9 was published in 1977 by the Department of Knowledge Management and Sharing of the World Health Organization. ICD-9 was an important transition to increased granularity with 4-digit-level categories and a variety of optional 5-digit subdivisions. It was also pivotal in moving the system out of the WHO once ICD became a part of the public domain. ICD-9-Clinical Modification (CM) was the next expansion in the United States. The intention was to allow diagnostic coding of inpatient, outpatient, and physician office (nonfacility) use. It was developed by the National Center for Health Statistics. The CM expansion provided an opportunity to capture enhanced morbidity data and to update more frequently. This system is updated on October 1 of each year. ICD-9-CM was by now a 3-volume set with the first 2 volumes pertaining to diagnostic codes and the third containing procedural codes, though the latter never gained the popularity and widespread use in the United States of those developed through the Current Procedural Terminology process. The Centers for Medicare and Medicaid Services (CMS) and the National Center for Health Statistics both contribute to the oversight of the ICD-9-CM.³ In 1983, the Inpatient Prospective Payment System was adopted to pay for hospital care in the Medicare program, which insures the elderly and those with chronic disease. ICD-9-CM volumes 1, 2, and 3 were used for assigning cases to the Diagnoses-Related Groups used to derive payment amounts.

The Tenth Edition.

Neuroradiologists might be surprised to learn that work on ICD-10 began >30 years ago. Historically, updates occurred approximately once per decade. The initial effort on ICD-10 concluded in 1992. The ICD-10-CM was then introduced for its annual process of review in 1992. ICD-10 is much more granular than ICD-9, with an expansion from 17,000 codes to approximately 155,000. US-based providers might be further surprised to find out that many other countries transitioned to some form of ICD-10 many years ago. For example, Canada introduced a modified system, ICD-10-CA, in 2000. The international version of ICD-10 is used in >100 countries for cause-of-death reporting and statistics. In 2003, the Health Insurance Portability and Accountability Act of 1996 named ICD-9 as the code set for reporting diagnoses and procedures in electronic administrative transactions.⁶ On January 16, 2009, the US Department of Health and Human Services published a regulation requiring the replacement of ICD-9 with ICD-10 as of October 1, 2013.

ICD-10-CM uses the same basic hierarchical structure as ICD-9-CM. The first 3 digits represent common traits, with each subsequent character providing greater specificity. ICD-10-CM is alphanumeric, with a possible 7 digits of specificity as opposed to the 5 digits of the ICD-9. An oddity is that the letter U is the only letter not used.⁷ Other noteworthy changes include the addition of information relevant to ambulatory and managed care and greatly expanded injury codes that reflect the site of injury. Given the dramatic changes occurring within organized medicine in 2013, some authors called for a delay in the implementation of ICD-10 from the original planned date of October 1, 2013.⁸ This idea gained greater traction when the American Medical Association formally adopted a policy that favored delaying implementation.^8,9 The original implementation date was extended by the Department of the Health and Human Services in the latter half of 2012 to October 1, 2014.¹⁰ There was continued discomfort regarding implementation of ICD-10 by the 2014 date. The Protecting Access to Medicare Act of 2014 was primarily considered in the context of providing a temporary patch for the sustainable growth rate.^11,12 Embedded within that legislation was a further delay in the implementation of ICD-10 until October 1, 2015.¹² Finally October 1, 2015, was the date that ICD-10-CM went live in the United States.