ICD-10-CM Coding Conventions

Coding conventions are the general rules for using a classification system that must be followed to ensure accurate and consistent coding. They are crucial for interpreting both the Alphabetic Index and the Tabular List (or Tables for procedures) correctly, guiding coders in selecting the most precise codes supported by documentation. Adherence to these guidelines is often required under regulations like HIPAA, making them vital for accurate reimbursement, data quality, and compliance. The instructions and conventions within the classification itself always take precedence over general coding guidelines.

Coding conventions are categorized for both diagnosis coding (ICD-10-CM) and procedure coding (ICD-10-PCS), each with its unique set of rules.

ICD-10-CM Coding Conventions

The ICD-10-CM Official Guidelines for Coding and Reporting, approved by the Cooperating Parties (AHA, AHIMA, CMS, and NCHS), detail these conventions. These guidelines are organized into sections, with Section I covering conventions, general coding guidelines, and chapter-specific guidelines applicable to all healthcare settings.

Key ICD-10-CM conventions include:

• Alphabetic Index and Tabular List The ICD-10-CM system is divided into an Alphabetic Index and a Tabular List. It is critical to never code directly from the Alphabetic Index without verifying the code in the Tabular List to ensure accuracy and specificity. The Alphabetic Index lists terms and corresponding codes alphabetically, while the Tabular List is an alphanumeric listing of codes divided into chapters based on body system or condition.

• Punctuation and Symbols

  • Parentheses ( ) are used in both the Alphabetic Index and Tabular List to enclose nonessential modifiers. These are supplementary words that may be present or absent in a diagnostic statement without affecting the assigned code.
  • Brackets [ ] are used in the Tabular List to enclose synonyms, alternative wording, or explanatory phrases. In the Alphabetic Index, they identify manifestation codes that must be used in conjunction with an underlying condition code, and these codes in brackets are always sequenced second.
  • Colons : are used in the Tabular List after an incomplete term that requires one or more modifiers following the colon to make it assignable to a specific category.

• Instructional Notes

  • “Includes” Notes appear immediately under a three-character code title to further define or provide examples of the content of the category.
  • “Excludes” Notes indicate that codes excluded from each other are independent.
    • Excludes1 means “NOT CODED HERE !” and indicates that the excluded code should never be used at the same time as the code above the Excludes1 note, typically when two conditions cannot occur together (e.g., a congenital form vs. an acquired form of the same condition).
    • Excludes2 means “Not included here” and indicates that the condition excluded is not part of the condition represented by the code, but a patient may have both conditions simultaneously. In this case, it is acceptable to use both codes together.
  • Etiology/Manifestation Convention (“Code First,” “Use Additional Code,” and “in diseases classified elsewhere”) applies to conditions with an underlying cause (etiology) and multiple body system manifestations. This convention requires the underlying condition (etiology) to be sequenced first, followed by the manifestation. A “use additional code” note will be found at the etiology code, and a “code first” note at the manifestation code. Manifestation codes often include “in diseases classified elsewhere” in their title and are never permitted to be used as a first-listed or principal diagnosis.
  • “Code Also” Note instructs that two codes may be required to fully describe a condition, but it does not provide sequencing direction; sequencing depends on the circumstances of the encounter.

• Terms and Abbreviations

  • The word “and” should be interpreted as “and/or” when it appears in a code title.
  • The word “with” or “in” should be interpreted to mean “associated with” or “due to” when it appears in a code title, the Alphabetic Index, or an instructional note, and often presumes a causal relationship.
  • “See” is a mandatory cross-reference in the Alphabetic Index indicating that another term must be referenced to locate the correct code.
  • “See Also” suggests that another main term may provide additional useful Alphabetic Index entries, but it is not necessary to follow it if the original main term provides the necessary code.
  • NOS (Not Otherwise Specified) is equivalent to “unspecified”.
  • NEC (Not Elsewhere Classifiable) means “other specified”. Coders should avoid “NOS” codes whenever possible and query the provider for more detail.
  • Placeholder Character ‘X’ is most often used in the fifth character position and in certain six-character code positions for future code expansion. It must be used when required for a code to be considered valid, especially when a 7th character is needed but the code is less than six characters.
  • 7th Character provides additional specificity for certain ICD-10-CM codes, particularly for injuries (S00-T88), indicating information about the encounter (initial, subsequent) and the healing process (e.g., routine healing, delayed healing, nonunion, malunion).
  • Default Codes are listed next to a main term in the Alphabetic Index and represent the condition most commonly associated with that term, or the unspecified code for the condition, to be assigned if no additional information is provided.

ICD-10-PCS Coding Conventions

The ICD-10-PCS Official Guidelines for Coding and Reporting are found in the front of the codebook and outline general and section-specific rules.

Key ICD-10-PCS conventions include:

• Seven Characters All ICD-10-PCS codes must consist of seven characters. Each character represents a distinct aspect of the procedure: Section, Body System, Root Operation, Body Part, Approach, Device, and Qualifier. If documentation is incomplete for coding purposes, the physician must be queried for the necessary information. The letters “I” and “O” are not used as values in any character position to avoid confusion with the numbers 1 and 0 .

• Alphabetic Index and Tables The ICD-10-PCS system uses an Alphabetic Index to direct coders to the appropriate table. However, it is not required to consult the index first before proceeding directly to the tables to complete the code. Valid codes include all combinations of choices in characters 4 through 7 contained in the same row of the table.

• Standardized Terminology Many terms used to construct PCS codes are defined within the system. It is the coder’s responsibility to determine what the documentation in the medical record equates to in the PCS definitions. Physicians are not expected to use the exact terminology found in PCS code descriptions, and coders are not required to query the physician when the correlation between documentation and PCS terms is clear. For example, “partial resection” correlates to “Excision”.

• Root Operations The root operation, defined by the third character, identifies the main objective and intent of the procedure performed. Each root operation has a precise, full definition that must be applied. Components or steps integral to a root operation’s definition (e.g., resecting a joint integral to joint replacement, steps to reach and close an operative site) are not coded separately.

• Multiple Procedures During the same operative episode, multiple procedures are coded if:

  • The same root operation is performed on different body parts (as defined by distinct body part character values).
  • The same root operation is repeated at different anatomic sites within the same body part value.
  • Multiple root operations with distinct objectives are performed on the same body part.
  • The intended root operation is attempted using one approach but is converted to a different approach (ee.g., laparoscopic converted to open requires two codes).

• Other Characteristics

  • The word “and” in a code description means “and/or,” except when describing a combination of multiple body parts for which separate values exist.
  • No Eponyms or Common Procedure Names are used in code descriptions; the system relies on root operations.
  • No Combination Codes are present in ICD-10-PCS; each procedure performed during an operative episode with a distinct objective is coded separately.
  • No Diagnostic Information is included in procedure code descriptions.
  • NOS (Not Otherwise Specified) code options are restricted, and NEC (Not Elsewhere Classified) options are limited.
  • New Technology Section (X codes) captures procedures involving new devices, substances, or technologies. These are standalone codes, meaning no additional code from other sections is needed to describe that specific new technology procedure.

Understanding and applying these coding conventions for both ICD-10-CM and ICD-10-PCS is fundamental for coders to ensure high standards of coding accuracy, compliance, and proper reimbursement in healthcare.