Coding Knowledge and Skills
Coding Knowledge and Skills is the largest domain on the CCS and decides most pass/fail outcomes. Items present facility scenarios - inpatient records coded in ICD-10-CM/PCS and outpatient records coded in ICD-10-CM plus CPT and HCPCS Level II - and test application of conventions, guidelines, and sequencing rather than recall of definitions.
Conventions that drive code assignment
- ICD-10-CM: locate the term in the Alphabetic Index, then verify the code in the Tabular List. Never code from the Index alone; the Tabular carries the instructions.
- Excludes1 means the two conditions are not reported together (an exception exists only when a guideline explicitly permits it). Excludes2 means both conditions may coexist and both may be coded.
- "Code first," "Use additional code," and "in diseases classified elsewhere" notes are mandatory, not suggestions.
- Seventh characters: injury episode (A initial, D subsequent, S sequela) and laterality/severity characters must match the record; use the unspecified character only when the detail is truly absent.
- ICD-10-PCS has seven characters and no decimal, and is built from Tables. The root operation definition controls the code - distinguish Excision from Resection, Drainage from Extirpation - not the surgeon's wording.
- CPT: code the documented procedure, site, and extent; append modifiers only when supported (26 professional component, TC technical component, 25 distinct E/M, 59 or X{EPSU} for distinct services, 50 bilateral, 62 co-surgery).
- Principal diagnosis (inpatient) is the condition established after study as chiefly responsible for admission (UHDDS). When two conditions meet the definition, either may be sequenced first; choose the one most related to the current episode.
Worked example
A 68-year-old with type 2 diabetes is admitted for a chronic ulcer of the right great toe with exposed fat layer. The Index entry for diabetic foot ulcer directs the coder to the diabetes code with an instruction to add the ulcer site code. Assign E11.621 (type 2 diabetes with foot ulcer) first, then L97.512 (non-pressure chronic ulcer of other part of right foot with fat layer exposed). Sequencing follows the "use additional code" instruction; laterality and severity are required characters, so an undocumented severity would force the unspecified seventh character and, ideally, a query.
Traps that cost marks
Coding from the Index without confirming Tabular instructions; confusing Excludes1 and Excludes2; coding "history of" conditions as active; assigning a more specific code than the documentation supports; assigning present-on-admission indicators to outpatient records (POA applies to inpatient claims only); and treating a physician's "probable" diagnosis as confirmed on an outpatient encounter.