ICD-10-CM
ICD-10 code for Mastocytosis aggressive systemic: C96.21
The ICD-10-CM index points "Mastocytosis aggressive systemic" to C96.21, Aggressive systemic mastocytosis. C96.21 is a billable code.
Source: CDC ICD-10-CM FY2027 Alphabetic Index file dated June 16, 2026. Publisher page
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More specific codes in C96
A header groups codes and is not billed. A billable code is one you can report.
- C96Other and unspecified malignant neoplasms of lymphoid, hematopoietic and related tissueHeader
- C96.0Multifocal and multisystemic (disseminated) Langerhans-cell histiocytosisBillable
- C96.2Malignant mast cell neoplasmHeader
- C96.20Malignant mast cell neoplasm, unspecifiedBillable
- C96.21Aggressive systemic mastocytosisBillable
- C96.22Mast cell sarcomaBillable
- C96.29Other malignant mast cell neoplasmBillable
- C96.4Sarcoma of dendritic cells (accessory cells)Billable
- C96.5Multifocal and unisystemic Langerhans-cell histiocytosisBillable
- C96.6Unifocal Langerhans-cell histiocytosisBillable
- C96.9Malignant neoplasm of lymphoid, hematopoietic and related tissue, unspecifiedBillable
- C96.AHistiocytic sarcomaBillable
- C96.ZOther specified malignant neoplasms of lymphoid, hematopoietic and related tissueBillable
Excludes1
Related conditions
Related pages
- C96.21 code detailsNotes, nearby codes, CMS-HCC group
- Category C96Every code under it
- Chapter 2Neoplasms
- ICD-10 codes by conditionA to Z
- Check a list of ICD-10 codes
- Denial code CO-11Diagnosis does not support the procedure
- Denial code CO-146Diagnosis invalid for the date of service
- HCPCS Level II code lookup
Questions
What is the ICD-10 code for Mastocytosis aggressive systemic?
The ICD-10-CM index points "Mastocytosis aggressive systemic" to C96.21, Aggressive systemic mastocytosis. C96.21 is a billable code.
Is C96.21 billable?
Yes. C96.21 is a billable code in the FY2027 ICD-10-CM file. Use a more specific code when the record documents one.
What documentation notes apply to C96.21?
The CDC tabular list gives 4 Excludes1 notes (not coded together) for C96.21 and the categories above it. They are listed on this page.
What chapter is C96.21 in?
Chapter 2. Neoplasms.
When do ICD-10-CM codes change?
Every October 1, with the new fiscal year file. Some years add April 1 updates. This page uses the FY2027 file, effective October 1, 2026.