ICD-10-CM (Clinical Modification)

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.

All Health Insurance Portability and Accountability Act (HIPAA)-covered entities must adhere to ICD-10-CM codes, as mandated by the U.S Department of Health and Human Services (HHS).

Importance of ICD-10-CM codes

ICD-10-CM codes are important because they are more granular than ICD-10 codes and can provide more information about the severity of a patient's condition.

The move to ICD-10-CM from ICD-9-CM was also necessitated by the fact that the latter was running out of code capacity to expand, as most of the code categories were completely full. Additionally, ICD-9-CM codes lacked the specificity and detail provided by ICD-10-CM.

FY2019 changes

ICD-10-CM has been revised frequently since 2003 -- even before it was formally adopted in the U.S. -- to keep up with alterations made to ICD-10 by WHO.

The 2019 ICD-10-CM codes became effective on Oct. 1, 2018, and should be used for discharges and patient encounters from that date through Sept. 30, 2019. The 2019 guidelines were approved by the four organizations that comprise the Cooperating Parties for ICD-10-CM: The Centers for Medicare & Medicaid Services (CMS), the National Center for Health Statistics (NCHS), the American Hospital Association (AHA) and the American Health Information Management Association (AHIMA).

The update contains 279 new codes and 143 revised codes and removes 51 codes, bringing the total number of codes to 71,932.

The new guidelines are organized into four sections as follows:

  • Section I: Conventions, general guidelines and chapter-specific guidelines;
  • Section II: Guidelines for selection of principal diagnosis for non-outpatient settings;
  • Section III: Guidelines for reporting additional diagnoses in non-outpatient settings; and
  • Section IV: Outpatient coding and reporting.

Code structure

The structure of ICD-10-CM codes is as follows: The first character must be an alpha character, excluding "u." The second and third characters are numeric, and characters four through seven can be a combination of numeric and alpha characters.

The first three characters categorize the injury, and the fourth through sixth characters describe in greater detail the cause, anatomical location and severity of an injury or illness. For certain codes, a seventh character is an extension digit and used to classify an initial, subsequent or sequela (late effect) treatment encounter. ICD-10-CM also uses a placeholder character "X" to allow for future expansion of certain codes.

CMS guidelines state that diagnosis codes are to be used and reported at their highest number of characters available and that three-character codes should only be used if it is not further subdivided. A code will be considered invalid if it has not been coded to the full number of characters required, including a seventh character if applicable.

ICD-10-CM is also divided into an alphabetical index and a tabular list. The alphabetical index is an alphabetical list of terms and the corresponding codes, and the tabular list is a structured list of codes that is divided into chapters that are based on a body system or condition.


See our Continue Reading section below for a link to the full list of ICD-10-CM codes. Some of the new codes included in the 2019 ICD-10-CM include:

  • F12.23 Cannabis dependence with withdrawal
  • F12.93 Cannabis use, unspecified with withdrawal
  • F53.0 Postpartum depression
  • G71.0 Muscular dystrophy
  • G71.00 Muscular dystrophy, unspecified
  • P04.14 Newborn affected by maternal use of opiates
  • P04.15 Newborn affected by maternal use of antidepressants
  • P35.4 Congenital Zika virus disease
  • T43.641 Poisoning by ecstasy, accidental (unintentional)
  • T43.641A Poisoning by ecstasy, accidental (unintentional), initial encounter
  • T43.641D Poisoning by ecstasy, accidental (unintentional), subsequent encounter
  • T43.641S Poisoning by ecstasy, accidental (unintentional), sequela
This was last updated in October 2018

Continue Reading About ICD-10-CM (Clinical Modification)

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