Successfully navigating the transition to ICD-10 terminology

The 10th revision of the International Classification of Diseases (ICD-10) took effect October 1 in the U.S. The change to ICD-10 allows you and your coders to capture more details about the health status of patients and sets the stage for improved patient care and public health surveillance across the country. As with any new government policy, law, standard, or code, questions are sure to arise. The American College of Surgeons (ACS) is taking steps to ease the transition to ICD-10 from ICD-9.

Glossary of terms

Besides the task of transitioning to ICD-10, surgeons and their staff should become familiar with new terminology to properly code with the expanded code set. Following is a useful glossary of ICD-10 terms to help ensure a smooth transition.

  • Alphabetic Index: An alphabetical list of ICD-10-CM (Clinical Modification) terms and their corresponding codes, which helps to determine which section to refer to in the Tabular List. It does not always provide the full code. The Alphabetic Index consists of the following parts: the Index of Diseases and Injury, the Index of External Causes of Injury, the Table of Neoplasms, and the Table of Drugs and Chemicals.
  • Acute conditions: Medical conditions characterized by sudden onset, severe change, and/or short duration.
  • Additional diagnosis: The secondary diagnosis code used, if available, to provide a more complete picture of the primary diagnosis.
  • Bilateral: For bilateral sites, the final character of the codes in the ICD-10-CM indicates laterality. An unspecified side code also is provided in instances where the side may be unidentified in the medical record. If no bilateral code is provided and the condition is bilateral, assign separate codes for both the left and right side.
  • Category: The three-digit diagnosis code classifications that broadly define each condition (for example, 250 for diabetes mellitus).
  • Character “x”: Used as a placeholder in ICD-10-CM in certain codes to allow for future expansion and to fill in empty characters when a code that is less than six characters in length requires a seventh character.
  • Chronic conditions: Medical conditions characterized by long duration, frequent recurrence over a long period of time, and/or slow progression over time.
  • Combination codes: Single codes used to classify any of the following: two diagnoses; a diagnosis with an associated secondary process (manifestation); or a diagnosis with an associated complication.
  • Conventions of ICD-10: The general rules for use of the classification independent of guidelines. These conventions are incorporated within the Index and Tabular List of the ICD-10-CM as instructional notes. Possible conventions to include with codes include the following:
    • Notes: Extra information to define or clarify code choice.
    • Includes notes: This note appears immediately under a three-character code title to further define or give examples of the content of the category.
    • Not otherwise specified (NOS): This abbreviation is the equivalent of “unspecified.”
    • Excludes notes: There are two types of excludes notes. A type 1 excludes (Excludes1) note means “not coded here.” An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition. A type 2 excludes (Excludes2) note indicates “not included here.” An Excludes2 note indicates that the condition excluded is not associated with the condition represented by the code, but a patient may have both conditions at the same time. When an Excludes2 note appears under a code, it is acceptable to use both the code and the excluded code together when appropriate.
    • Not elsewhere classifiable (NEC): This abbreviation in the Tabular List represents “other specified.” When a specific code is not available for a condition the Tabular List includes an NEC entry under a code to identify the code as the “other specified” code.
  • Documentation: Clinical documentation specificity is one of the most important characteristics of the ICD-10-CM coding system. Additional details in clinical documentation provide more information, suggestions, guidance, and checklists—all of which coding professionals may use to select the codes that most accurately describe the procedures and services provided.1
  • GEM (General Equivalence Mapping): This reference mapping attempts to include all valid relationships between the codes in the ICD-9-CM diagnosis classification and the ICD-10-CM diagnosis classification. It is a useful tool to convert data from ICD-9-CM to ICD-10-CM.2
  • ICD: A medical code set maintained by the World Health Organization (WHO). The primary purpose of this code set is to classify both causes of death or mortality and diseases or morbidity. The U.S. extension, known as ICD-CM, is maintained by the National Center for Health Statistics within the Centers for Disease Control and Prevention to more precisely define ICD use in the U.S. ICD-10 is represented with a letter in the first position and a number in the second, third, and fourth positions. The fourth character follows a decimal point. Possible code numbers range from A00.0 to Z99.9.  The letter U is not used.3
  • Index (to diseases): The ICD-10-CM is divided into the Alphabetic Index described earlier and the Tabular List.
  • Manifestation codes: Certain conditions have both an underlying etiology and multiple body system manifestations. For such conditions, the ICD-10-CM has a coding convention that requires the underlying condition be sequenced first followed by the manifestation. Wherever such a combination exists, there is a “use additional code” note at the etiology code, and a “code first” note at the manifestation code. These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation.
  • Medical necessity: Services or supplies that are proper and needed for the diagnosis or treatment of a medical condition; are provided for the diagnosis, direct care, and treatment of a medical condition; meet the standards of good medical practice in the local area; and are not mainly for the convenience of the patient or physician.
  • Morbidity: Term refers to the disease rate or number of cases of a particular disease in a given age range, gender, occupation, or other relevant population-based grouping.
  • Principal diagnosis: First-listed/primary diagnosis code. The code sequenced first on a medical record defines the primary reason for the encounter as determined at the end of the encounter.
  • Signs/symptoms: Codes that describe symptoms and signs, as opposed to diagnoses, are acceptable for reporting purposes when a related definitive diagnosis has not been established (confirmed) by the provider.
  • Sequelae: A late effect is the residual effect (condition produced) after the acute phase of an illness or injury has terminated. There is no time limit on when a late effect code can be used. The residual may be apparent early, such as in cerebral infarction, or it may occur months or years later, such as that due to a previous injury.
  • Tabular List: A chronological list of ICD-10-CM codes divided into chapters based on body system or condition. It is essential to use both the Alphabetic Index and Tabular List when locating and assigning a code. The Alphabetic Index does not always provide the full code. Selection of the full code, including laterality and any applicable seventh character, can only be done in the Tabular List. A dash (-) at the end of an alphabetic index entry indicates that additional characters are required. Even if a dash is not included at the Alphabetic Index entry, it is necessary to refer to the Tabular List to verify that no seventh character is required.4 


  1. American Medical Association. CPT Assistant, Clinical Documentation Assessment: Looking at the patterns between the ICD-9-CM and ICD-10-CM coding systems. Available at: Accessed October 2, 2015.
  2. American Health Information Management Association. Putting the ICD-10-CM/PCS GEMs into practice. Available at: Accessed October 2, 2015.
  3. World Health Organization. iCAT glossary. Available at: Accessed October 2, 2015.
  4. New Hanover Regional Medical Center. ICD-10 glossary of terms. Available at: Accessed October 2, 2015.

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