ICD-10 Code C84.9 – Mature T/NK-cell lymphomas, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C84.9 – Mature T/NK-cell lymphomas, unspecified
What it is
C84.9 identifies a mature T-cell or natural killer-cell lymphoma when the record does not specify a more exact subtype. Use it for a confirmed lymphoma diagnosis involving mature T/NK cells, but with limited detail.
Clinical signs
Clinical features vary; refer to documentation. Commonly, these lymphomas present as lymphadenopathy, systemic symptoms, or extranodal disease, but the specific pattern depends on the subtype and site involved.
When to use this code
Use C84.9 when the provider documents a mature T/NK-cell lymphoma and does not name a more specific category. It also fits when pathology confirms the lineage, but the subtype remains unspecified in the final report. If the record later identifies a precise lymphoma type, code that instead.
Do not use for
Do not use this code for Hodgkin lymphoma, B-cell lymphomas, or reactive lymphoid disorders. If the documentation names a specific mature T-cell or NK-cell lymphoma, check documentation and code the exact diagnosis.
Coding tip
Query for the exact lymphoma subtype whenever the note only says “T-cell lymphoma” or “NK-cell lymphoma.”