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ICD-10-CM 2027

ICD-10 code for aggressive systemic mastocytosis

C96.21

Aggressive systemic mastocytosis

✓ Billable / specificCC — complication/comorbidity

From the official ICD-10-CM alphabetic index entry “Mastocytosis › aggressive systemic”. Page updated September 29, 2026.

About coding aggressive systemic mastocytosis

The ICD-10-CM code for aggressive systemic mastocytosis is C96.21 (Aggressive systemic mastocytosis).

Within C96.2 (malignant mast cell neoplasm), C96.21 is specifically for aggressive systemic mastocytosis. Related codes cover unspecified (C96.20), mast cell sarcoma (C96.22) and other malignant mast cell neoplasm (C96.29).

As a secondary diagnosis it is a CC (complication or comorbidity), which can move an inpatient stay into the "with CC" MS-DRG of its family, unless the principal diagnosis excludes it.

In MS-DRG v44.0, it is part of the grouping logic for DRG 011 (Tracheostomy for Face, Mouth and Neck Diagnoses or Laryngectomy with MCC, relative weight 5.6154), DRG 012 (Tracheostomy for Face, Mouth and Neck Diagnoses or Laryngectomy with CC, relative weight 4.381), DRG 013 (Tracheostomy for Face, Mouth and Neck Diagnoses or Laryngectomy without CC/MCC, relative weight 2.7307), DRG 820 (Lymphoma and Leukemia with Major O.R. Procedures with MCC, relative weight 6.2481), DRG 821 (Lymphoma and Leukemia with Major O.R. Procedures with CC, relative weight 2.2023), DRG 822 (Lymphoma and Leukemia with Major O.R. Procedures without CC/MCC, relative weight 1.1272) and 6 more, in Pre-MDC and MDC 17 (Myeloproliferative Diseases and Disorders, Poorly Differentiated Neoplasms), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

Common questions about aggressive systemic mastocytosis ICD-10 codes

What is the ICD-10 code for aggressive systemic mastocytosis?

C96.21 — Aggressive systemic mastocytosis.

Is C96.21 billable?

Yes. C96.21 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).

Can C96.21 be used as a principal diagnosis?

Yes. The Medicare Code Editor doesn't restrict C96.21 as a principal diagnosis.

Is C96.21 a CC or MCC?

C96.21 is a CC (complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.