C96.21 – Aggressive systemic mastocytosis

ICD-10-CM 2027 diagnosis code · Malignant neoplasms of lymphoid, hematopoietic and related tissue

Billable code

ICD-10-CM code C96.21

Code: C96.21 (claims format: C9621)
Description: Aggressive systemic mastocytosis
Billable: Yes – valid for HIPAA-covered transactions
Valid for: Dates of service October 1, 2026 – September 30, 2027 (FY2027)
Chapter: 2. Neoplasms (C00-D49)
Block: C81-C96 Malignant neoplasms of lymphoid, hematopoietic and related tissue
Parent codes: C96 › C96.2

Notes inherited from parent codes

Instructional notes at a category or block level apply to every code below it.

C96 – Other and unspecified malignant neoplasms of lymphoid, hematopoietic and related tissue

Excludes1 (not coded here):

personal history of other malignant neoplasms of lymphoid, hematopoietic and related tissues (Z85.79)

C96.2 – Malignant mast cell neoplasm

Excludes1 (not coded here):

indolent mastocytosis (D47.02)
mast cell leukemia (C94.30)
mastocytosis (congenital) (cutaneous) (Q82.2)

Block C81-C96

Excludes2 (not included here):

Kaposi's sarcoma of lymph nodes (C46.3)
secondary and unspecified neoplasm of lymph nodes (C77.-)
secondary neoplasm of bone marrow (C79.52)
secondary neoplasm of spleen (C78.89)

Index terms for C96.21

Entries in the ICD-10-CM alphabetic index that lead to this code:

Mastocytosis, aggressive systemic

Related codes in C96.2

C96.20 – Malignant mast cell neoplasm, unspecifiedBillable
C96.22 – Mast cell sarcomaBillable
C96.29 – Other malignant mast cell neoplasmBillable

Frequently asked questions

What is ICD-10 code C96.21?

C96.21 is the ICD-10-CM code for aggressive systemic mastocytosis, in the block C81-C96 (Malignant neoplasms of lymphoid, hematopoietic and related tissue).

Is C96.21 a billable code?

Yes. C96.21 is a billable/specific code that can be used to indicate a diagnosis for reimbursement purposes.

What category does C96.21 belong to?

It belongs to category C96 – Other and unspecified malignant neoplasms of lymphoid, hematopoietic and related tissue.

Source: CDC/NCHS ICD-10-CM FY2027 code files, tabular list and index. Reference only – code assignment must follow the official ICD-10-CM guidelines and documentation in the medical record.