ICD-10-CM Diagnosis Coding
Core concepts
ICD-10-CM uses a tabular list and an alphabetic index, with the index as the entry point and the tabular list as verification. Candidates must apply the official guidelines in order: conventions, general guidelines, and chapter-specific guidelines. Understand the difference between Excludes1 (not coded together; mutually exclusive) and Excludes2 (not included here; may be coded together if documented). Know the meaning of "code also," "code first," "use additional code," and "see also" instructions.
Specificity and structure
Codes are up to seven characters. The seventh character often indicates encounter type (A = initial, D = subsequent, S = sequela). Placeholder "X" preserves character positions. Combination codes capture multiple conditions in one code. Sequela codes require coding the residual condition first, then the cause.
Traps to watch
- Coding from the index alone without verifying in the tabular list.
- Ignoring Excludes1 notes and coding mutually exclusive conditions together.
- Missing the seventh character for injuries or obstetric codes.
- Coding a symptom when a definitive diagnosis is documented (or vice versa).
- Failing to code laterality or encounter type when required.
Rule of thumb
Always verify the code in the tabular list. If the index entry has an instruction (e.g., "see category"), follow it-never shortcut.
Worked example
A patient presents with a new fracture of the right wrist after a fall. You code the fracture with the correct laterality and seventh character A (initial encounter), plus an external cause code. If the patient returns for follow-up healing, the seventh character changes to D (subsequent encounter).