C94.3 (Mast cell leukemia) compared with D89.40 (Mast cell activation, unspecified), from the official CMS tabular data. Do not report these codes together: the official tabular list marks them Excludes1.
Not coded here — these two are mutually exclusive.
“mast cell leukemia (C94.3-)”
An Excludes1 note means the two conditions cannot occur together, so the pair should not be reported for the same encounter. The sole exception is when the conditions are documented as unrelated to each other.
Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a
No — do not report together. D89.40 carries an Excludes1 note covering C94.3: “mast cell leukemia (C94.3-)”
Sole exception: when the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).
| C94.3Mast cell leukemia | D89.40Mast cell activation, unspecified | |
|---|---|---|
| Billing status | Non-billable header | Billable |
| Classification | C00-D49 — Neoplasms (C00-D49) | D50-D89 — Diseases of the Blood and Blood-forming Organs and Certain Disorders Involving the Immune Mechanism (D50-D89) |
| Definition | Mast cell leukemia is a non-billable ICD-10-CM category code (C94.3). | Mast cell activation, unspecified is a billable ICD-10-CM diagnosis code (D89.40). |
| Includes | — | defects in the complement system immunodeficiency disorders, except human immunodeficiency virus [HIV] disease sarcoidosis Mast cell activation disorder, unspecified |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources