Excludes1 pair
C84- vs C84.9-
C84 and C84.9 are not coded together. ICD-10-CM declares them mutually exclusive with an Excludes1 note — the two conditions are not expected to occur together, so exactly one of them is normally correct for a given encounter. The Official Guidelines carve out one exception: if the two conditions are clearly unrelated to each other, both may be reported.
The official note, declared on C84.9
mature T-cell lymphoma, not elsewhere classified (C84.4-)
C84.9
Mature T/NK-cell lymphomas, unspecified
Not billable
- Chapter 2
- Neoplasms
- Section
- C81-C96
Use when the record says
- NK/T cell lymphoma NOS
Indexed under
- Lymphoma › mature T/NK-cell
- Lymphoma › NK/T cell
Excludes1 is not always absolute: where two conditions covered by the note are genuinely unrelated, CMS guidance permits reporting both. Document the reasoning rather than assuming it. More on Excludes1 vs Excludes2 · FY2027