The tenth edition of the International Classification of Diseases or “ICD-10” is used to categorize and catalog health conditions and diseases with specific conditions, as well as subtly differentiated diseases that are associated with broader morbidities.

Many countries use their own national variation of ICD-10 with key modifiers to align with their unique healthcare infrastructure. The variation used in the United States is published by the Centers for Medicare & Medicaid Services (CMS), along with the National Center for Health Statistics (NCHS) and is called ICD-10-CM or International Classification of Diseases, Tenth Revision, with Clinical Modification.

CMS also produces a distinct procedural classification called ICD-10-PCS or International Classification of Diseases, Tenth Revision, Procedure Coding System, which is used in a hospital setting or other medical facilities that provide inpatient procedures.

ICD-10-CM’s goal is to provide a standardized system of classification for:

Diagnosis of conditions & common diseases
Related health problems
Reporting abnormal findings
Reporting signs and symptoms
Diagnosing injuries
Noting the external causes of injuries and diseases
Noting social circumstances that may contribute to injuries and diseases

The accurate use of ICD-10-CM codes plays a critical role in ensuring that a provider receives proper reimbursement for medical services provided to patients. Payer organizations like insurance companies and public health institutions require the use of accurate ICD-10-CM codes to honor a claim for reimbursement.

The History of ICD

Though the long history of the ICD system can be traced all the way back to the 1850s when it was known as the International List of Causes of Death. It was eventually standardized in 1893 by the International Statistical Institute.

The World Health Organization took control and oversight of the International Classification of Diseases in 1948 to encourage international standardization throughout all healthcare systems in various countries that choose to participate.

At that time, the WHO saw ICD as a superior means of tracking diseases and a possible means to eliminate them within differing populations. As ICD took hold and proved its effectiveness on a global scale, it began to expand with new updated versions published. The most notable version being the Sixth Revision ICD-6, included causes of morbidity.

WHO thought it quickly evolved and released an updated ICD-7 in 1957 and the ICD-8 in 1968. The WHO released ICD-9 in 1975 and the United States published ICD-9-CM in 1979, as a better way to capture enhanced morbidity data. It also integrated a wide range of common surgical procedures as well as other treatments that were being classified by hospitals across North America.

One of the unique features of ICD-9-CM is that it was updated annually by CMS and the NCHS. It soon expanded into a three-volume set, with two volumes that were dedicated to diagnosis codes and the third volume was published containing inpatient procedural codes.

ICD-10 was released in 1990 by the WHO. ICD-10-CM was first released in 1992 but took until 2013 for ICD-10-CM to become implemented in the US. ICD-10-CM no longer included the third volume of inpatient procedure codes and the omitted inpatient procedure codes were outsourced to 3M’s Health Information Systems to create the initial version of ICD-10-PCS.

When Are ICD-10-CM and ICD-10-PCS Used?

ICD-10-CM and ICD-10-PCS are vastly different in their content, use and their setting.

ICD-10-PCS — procedure code set used only in hospital inpatient settings
ICD-10-CM — primarily for diagnosis codes in any healthcare setting.

Changes in Codes from ICD-9-CM to ICD-10-CM

One of the biggest updates from ICD-9 to ICD-10 is the ability to better compare and analyze morbidity and mortality data. This includes morbidity diagnosis and procedural data at the state and national levels. It also makes it more feasible to analyze mortality data and compare it nationally or even internationally.

The codes used in ICD-10-CM have greater specificity than the older ICD-9-CM codes. This allows for a more detailed classification of a person’s health conditions, diseases, and injuries. It enables clinicians and medical coders to describe the anatomy, etiology, and potential complications that person is experiencing with better accuracy and therefore distinction. It also allows for a greater detailed description of any comorbidities that could be influencing a person’s condition as well as the severity of illnesses.

The Benefits of ICD-10’s Specificity

ICD-10-CM has roughly 72,000 available codes whereas ICD-9-CM has just 13,000 diagnosis codes. This ability to more accurately describe a condition underscores the real-world clinical environment and the sweeping recent advancements in modern medical technology. Of course, it also means that clinicians and medical coders throughout the healthcare industry need to be diligent about using the correct code for services rendered.

The massive increase in the volume of codes and the specificity gives providers and medical coders the ability to:

Accurately assess the efficacy of a patient’s care
Ensure patient safety in their care plan
Assess the health status and risk factors
Assess the patient’s healthcare costs
Prevent abusive coding and billing practices
The ability to analyze morbidity and mortality data

How Are ICD-10-CM Codes Structured?

ICD-10-CM codes have three to seven characters with each code starting with an alpha character, which indicates the chapter to which the code is found.

The second and third characters in an ICD-10-CM code are numbers. Beyond that, the fourth through seventh characters can be numbers or letters. Only a small number of ICD-10-CM codes use a 7th character, and usually only find it if the characters serve a specific purpose, such as signifying laterality or defining whether the code is for an initial encounter of the problem, a subsequent encounter, or it is related to another condition.

Not all ICD-10-CM codes are supposed to be used to code patient data. ICD-10-CM codes should be used at the highest level of specificity. For example, the code C45 Mesothelioma should not be used and instead one of the 5 subtypes should be selected.

ICD-10-CM Provides Annual Updates

Another important strength of ICD-10-CM is that it was designed to be able to evolve. Every year ICD-10-CM and ICD-10-PCS are reviewed and updates are published by the ICD-10-CM/PCS Coordination and Maintenance Committee. This allows ICD-10-CM to continue to grow and evolve with the times as new medical techniques and technology become available.

Coming Soon — ICD-11

ICD-11 was officially endorsed by the WHO in 2019 but has not yet been implemented in the US. ICD-11 is almost five times larger than ICD-10, with more than 120,000 codeable terms, and includes a smart coding algorithm that can now post-coordinate more than 1.6 million terms. As of 2022, 35 countries are using ICD-11 for causes of death, cancer registration, patient safety, allergology, clinical documentation, dermatology, reimbursement and more such as rare diseases, perinatal and maternal coding that assists with recording and reporting mortality & morbidity statistics.

What is ICD-10?