D89.40 Mast cell activation, unspecified

Billable ICD-10-CM code, FY2026.

Applicable to

• Mast cell activation disorder, unspecified
• Mast cell activation syndrome, NOS

Applies from D89 Other disorders involving the immune mechanism, not elsewhere classified

Excludes1 (never code together)

• hyperglobulinemia NOS (R77.1)
• monoclonal gammopathy (of undetermined significance) (D47.2)

Excludes2 (not included here)

• transplant failure and rejection (T86.-)

Applies from D89.4 Mast cell activation syndrome and related disorders

Excludes1 (never code together)

• aggressive systemic mastocytosis (C96.21)
• congenital cutaneous mastocytosis (Q82.2)
• (non-congenital) cutaneous mastocytosis (D47.01)
• (indolent) systemic mastocytosis (D47.02)
• malignant mast cell neoplasm (C96.2-)
• malignant mastocytoma (C96.29)
• mast cell leukemia (C94.3-)
• mast cell sarcoma (C96.22)
• mastocytoma NOS (D47.09)
• other mast cell neoplasms of uncertain behavior (D47.09)
• systemic mastocytosis associated with a clonal hematologic non-mast cell lineage disease (SM-AHNMD) (D47.02)

Risk adjustment (HCC)

• CMS-HCC V22: HCC 47 — Disorders of Immunity
• RxHCC V08: HCC 99 — Immune Disorders
• ESRD V24: HCC 47

MS-DRG index

Defines the logic of DRG(s) 814-816 in MDC 16.

Approximate ICD-9-CM (GEMs)

• 279.8 Other specified disorders involving the immune mechanism (approximate)

Code annotations containing back-references to D89.40

Back-references to D89

• Type 1 Excludes: D72 Other disorders of white blood cells ("immunity disorders (D80-D89)")

Diagnosis Index entries for D89.40

• Activation › mast cell (disorder) (syndrome)

Nearby codes

• D89.0 Polyclonal hypergammaglobulinemia
• D89.1 Cryoglobulinemia
• D89.2 Hypergammaglobulinemia, unspecified
• D89.3 Immune reconstitution syndrome
• D89.4 Mast cell activation syndrome and related disorders
• D89.40 Mast cell activation, unspecified (this code)
• D89.41 Monoclonal mast cell activation syndrome
• D89.42 Idiopathic mast cell activation syndrome
• D89.43 Secondary mast cell activation
• D89.44 Hereditary alpha tryptasemia
• D89.49 Other mast cell activation disorder