ICD-10-CM 101: A guide to the international classification system

Need a brief refresher on the basics of the ICD-10-CM classification system and how it works? We’ve got you covered. Take a few minutes to brush up on the international guide with our ICD-10-CM 101 guide.

Table of Contents

What is the ICD-10-CM?

ICD-10-CM stands for International Classification of Diseases, 10th Revision, Clinical Modification. The ICD-10-CM is based on the ICD-10, or the International Statistical Classification of Diseases and Related Health Problems, 10th Revision. Internationally, the World Health Organization (WHO) is the authoritative source for this guide. In the United States, the National Center for Health Statistics (NCHS), part of the Centers for Disease Control and Prevention (CDC), creates a country-specific modification of the international guide, known as the ICD-10-CM.

Why is the ICD-10-CM used?

The codes within the ICD-10-CM represent medical diagnoses and other related information. For example, instead of just documenting that a patient had a heart attack, the ICD-10-CM codes allow providers to specify that a patient had a heart attack at home while working outside – among other location- and activity-based specifications. This patient information ultimately goes into an electronic health record (EHR). With this EHR integration, ICD-10-CM codes help facilitate important tasks, such as generating healthcare statistics, monitoring quality outcomes and mortality statistics, and generating billing claims.

How is the ICD-10-CM maintained?

The ICD-10-CM Coordination and Maintenance Committee is responsible for maintaining and updating ICD-10-CM. Twice a year, the Committee holds meetings in which members of the public are able to give input on new code changes and proposals. The Committee has the authority to update the system with new codes that become effective on either April 1st or October 1st, but typically system updates are made available on the October date, with April updates often reflecting more time-sensitive releases.

What do ICD-10-CM codes look like?

ICD-10-CM codes are seven-character, alphanumeric codes. The first character is a letter followed by two numbers that represent the category of injury or disease. This is followed by a decimal point and four more characters that can be either alphabetic or numeric.

ICD-9-CM to ICD-10 to ICD-11

On October 1, 2015, CMS transitioned from ICD-9-CM to ICD-10-CM, 23 years after the WHO released the first international ICD-10 codes. The United States Department of Health and Human Services released a final rule on January 12, 2009 that outlined implementation timeframes for any organization covered by HIPAA to adopt the ICD-10-CM for medical coding. At the time, the US was the only industrialized nation not using an ICD-10 classification-based system, yet it still took another six years after publishing these rules for the US to begin using the system. More recently, on June 18, 2018, the WHO released a version of the ICD-11, which was the result of over a decade of planning. The new version, currently under review by WHO member nations, is completely electronic and will become effective on January 1, 2022 for international death certificate reporting.

Looking for resources on other code systems? Check out our 101 guides to Current Procedural Terminology (CPT), Systemized Nomenclature of Medicine – Clinical Terms (SNOMED CT), and Logical Observation Identifiers Names and Codes (LOINC).

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