How to Find the Right ICD-10-CM Code
The two-step ICD-10-CM lookup the Official Guidelines require - locate the term in the Alphabetic Index, then verify it in the Tabular List - plus NEC, NOS, default codes and specificity.
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Short answer
Look up the main term in the ICD-10-CM Alphabetic Index, follow its subterms and cross-references to a code, then verify that code in the Tabular List, reading every instructional note, before you report it. Report the code at the full number of characters required, and use unspecified codes only when the record does not support more detail.
Key takeaways
- Never code from the Alphabetic Index alone. Verify every code in the Tabular List (Official Guidelines, Section I.B.1).
- Main terms in the Index are usually the condition, not the body site.
- NEC means "not elsewhere classifiable" (a specific condition with no specific code); NOS means "not otherwise specified" (unspecified).
- A code is invalid if it does not have the full number of characters required.
ICD-10-CM has two parts that work together: the Alphabetic Index, an alphabetical list of terms with their codes, and the Tabular List, the chronological list of codes divided into chapters by body system or condition. The Official Guidelines expect you to use both, in that order.
Step 1: Pick the main term from the documentation
Read the record and identify the condition being coded. In the Alphabetic Index, main terms are usually the condition (for example, "fracture", "pneumonia", "laceration"), not the anatomical site. The site is normally a subterm under the condition.
The Index has separate sections that matter for specific situations: the Table of Neoplasms, the Table of Drugs and Chemicals, and the External Cause of Injuries Index.
Step 2: Follow subterms, cross-references and conventions in the Index
- Subterms (indented under the main term) add site, type or cause. Work down until the entry matches the documentation.
- "See" directs you to another term; you must go there. "See also" points to another entry that may be useful, but is optional when the current entry already fits.
- Nonessential modifiers in parentheses after a term do not change the code; they may be present or absent in the record.
- A code followed by a dash (for example, E11.-) means the code is incomplete and more characters are needed from the Tabular List.
- Default code: the code next to a main term is the one most commonly associated with that term, or the unspecified code. Use it when the record has no further detail.
Step 3: Verify the code in the Tabular List
Locate the code in the Tabular List and confirm it matches the documentation (Section I.B.1). While you are there, read:
- The Includes notes and inclusion terms that describe what the code covers.
- Excludes1 and Excludes2 notes, at the code and every level above it.
- Code first, Use additional code and Code also notes that affect which codes are needed and their order.
- Any 7th character requirement for the category.
On ICD Code Finder, each code page gathers these in one place: inclusion terms, all instructional notes (own and inherited, with the source code shown), the 7th character table, parent and child codes, and links back to the chapter and block.
Step 4: Code to the highest level of specificity
A code is invalid if it has not been coded to the full number of characters required for that code, including the 7th character when applicable. Report a three-character code only if it is not further subdivided.
Specificity also means using the detail the documentation supports:
- NEC ("not elsewhere classifiable") is used when the record specifies a condition but there is no specific code for it, so it is classified to an "other specified" code.
- NOS ("not otherwise specified") is the equivalent of unspecified. Use it only when the record lacks the detail for a more specific code.
When the record is unclear or conflicting, query the provider rather than choosing between codes yourself.
Step 5: Confirm the code is valid for the date of service
ICD-10-CM changes every fiscal year on October 1, and codes can be added, revised or deleted. Make sure the code is valid in the code set for the date of service. ICD Code Finder shows "New" and "Revised" badges on code pages and lists every change on the FY updates page.
Frequently asked questions
Why can't I code straight from the Alphabetic Index?
The Index does not show the instructional notes, 7th character requirements or the full set of more specific codes. The Official Guidelines require you to locate each term in the Index and then verify the code in the Tabular List.
What is a default code in ICD-10-CM?
The code listed next to a main term in the Alphabetic Index is the default code. It represents the condition most commonly associated with the main term, or is the unspecified code for the condition, and is used when the record documents the condition without more detail.
When is an unspecified code acceptable?
When the documentation does not support a more specific code. Unspecified codes are appropriate when information about a more specific condition is not known or not documented, though querying the provider is often the better option.
What does NEC mean?
Not elsewhere classifiable. It is used when the record gives a specific condition but ICD-10-CM has no specific code for it, so it falls into an "other specified" code.
Informational, not coding advice. This page summarizes ICD-10-CM conventions for education. Always code from the medical record using the current ICD-10-CM Tabular List, Alphabetic Index and Official Guidelines for Coding and Reporting, plus payer policy.
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