C84 vs C84.9
C84 and C84.9 can never be reported together. ICD-10-CM declares them mutually exclusive with an Excludes1 note, meaning the two conditions cannot occur in the same patient — so exactly one of them is correct for any given encounter.
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 (of) (malignant)
- Lymphoma › NK/T cell (of) (malignant)
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