The ICD-10-CM (International Classification of Diseases, Tenth Revision, Clinical Modification) is a system used by physicians and other healthcare providers to classify and code all diagnoses, symptoms and procedures recorded in conjunction with hospital care in the United States. It provides a level of detail that is necessary for diagnostic specificity and morbidity classification in the U.S.

Like its predecessor ICD-9-CM, ICD-10-CM is based on the International Classification of Diseases, which is published by the World Health Organization (WHO) and which uses unique alphanumeric codes to identify known diseases and other health problems. According to WHO, physicians, coders, health information managers, nurses and other healthcare professionals also use ICD-10-CM to assist them in the storage and retrieval of diagnostic information. ICD records are also used in the compilation of national mortality and morbidity statistics.

ICD-10-CM is a seven-character, alphanumeric code. Each code begins with a letter, and that letter is followed by two numbers. The first three characters of ICD-10-CM are the “category.” The category describes the general type of the injury or disease. The category is followed by a decimal point and the subcategory. This is followed by up to two sub-classifications, which further explain the cause, manifestation, location, severity, and type of injury or disease. The last character is the extension.

The extension describes the type of encounter this is. That is, if this is the first time a healthcare provider has seen the patient for this condition/injury/disease, it’s listed as the “initial encounter.” Every encounter after the first is listed as a “subsequent encounter.” Patient visits related to the effects of a previous injury or disease are listed with the term “sequela.”