ICD-10 Code C84.90 – Mature T/NK-cell lymphomas, unspecified, unspecified site (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C84.90 – Mature T/NK-cell lymphomas, unspecified, unspecified site
What it is
C84.90 identifies a mature T-cell or natural killer (NK)-cell lymphoma when the subtype and site are not specified. Use it for a documented lymphoma diagnosis that remains unclassified in the record.
Clinical signs
Clinical features vary; refer to documentation. These lymphomas may present with lymphadenopathy, systemic “B” symptoms, skin findings, or extranodal disease, but the exact pattern depends on the specific subtype.
When to use this code
Use this code when the provider documents a mature T/NK-cell lymphoma but does not name a more specific subtype or primary site. It is appropriate when the chart confirms lymphoma, yet the available record is incomplete. If later documentation identifies the subtype or site, code the more specific diagnosis instead.
Do not use for
Do not use C84.90 when the record specifies a different lymphoma type, such as B-cell lymphoma, Hodgkin lymphoma, or a named mature T/NK-cell subtype. Check documentation if the site or histology is stated elsewhere.
Coding tip
Query for the exact lymphoma subtype and site before assigning C84.90, because more specific documentation usually supports a more precise code.