ICD-10-CM Diagnosis Coding Conventions and Guidelines
This domain checks whether you apply the ICD-10-CM Official Guidelines for Coding and Reporting rather than simply matching a word in the index. Expect items on conventions, sequencing, combination codes, seventh characters, and the outpatient rule that you code only conditions documented as confirmed.
Two books, always in order
- Alphabetic Index first to locate the term; Tabular List second to verify and capture full specificity. Never code from the index alone - the index omits laterality and encounter characters.
- Index conventions: bold type means a code is assigned; non-bold type is a cross-reference (see, see also); brackets enclose manifestation codes that follow the etiology code; omit code means no code is assigned.
- Tabular conventions: Excludes1 means not coded here (the two conditions are mutually exclusive - never report both); Excludes2 means not included here (both may be reported if documented); code first indicates the underlying condition is sequenced first; use additional code means a secondary code is mandatory; parentheses enclose nonessential modifiers; and means and/or; with means linked even when the word with is not used.
Specificity and characters
- Seventh characters are required in chapters 13, 19, and 20 and elsewhere: A initial encounter, D subsequent encounter while healing, S sequela.
- Placeholder X keeps character positions correct when a character is empty.
- Unspecified codes are valid but must never replace a more specific code the record supports.
Code only what is documented
- Outpatient: do not code probable, suspected, rule out, or working diagnosis - code the signs and symptoms instead. Inpatient: a documented probable condition may be coded as if established.
Worked example
A 65-year-old with type 2 diabetes and stage 3b chronic kidney disease, plus COPD with acute bronchitis.
- Diabetes with CKD: index Diabetes, type 2, with, chronic kidney disease gives E11.22. The Tabular note directs use additional code to identify the stage of CKD, so N18.32 is added and E11.22 is sequenced first.
- COPD with acute bronchitis: index Bronchitis, acute, with COPD gives J44.0, whose note says code first the acute lower respiratory infection. J20.9 is sequenced first, J44.0 second.
Traps that cost marks
- Coding from the index without Tabular verification, producing a missing seventh character.
- Reporting both sides of an Excludes1 pair.
- Ignoring a use additional code note and under-reporting.
- Using a history Z code when the condition is current, or vice versa.
- Defaulting to unspecified instead of querying for laterality or type.
- Forgetting that the first-listed diagnosis is the reason for the encounter, not the most severe condition.