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D47.09 vs D89.42

D47.09 (Other mast cell neoplasms of uncertain behavior) compared with D89.42 (Idiopathic mast cell activation syndrome), from the official CMS tabular data. Do not report these codes together: the official tabular list marks them Excludes1.

Relationship

Conflict

Excludes1 conflict

D89.42
Idiopathic mast cell activation syndrome
↔
D47.09
Other mast cell neoplasms of uncertain behavior

Not coded here — these two are mutually exclusive.

“mastocytoma NOS (D47.09)”

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

Conflict

Excludes1 conflict

D89.42
Idiopathic mast cell activation syndrome
↔
D47.09
Other mast cell neoplasms of uncertain behavior

Not coded here — these two are mutually exclusive.

“other mast cell neoplasms of uncertain behavior (D47.09)”

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

Can these codes be reported together?

No — do not report together. D89.42 carries an Excludes1 note covering D47.09: “mastocytoma NOS (D47.09)”

Sole exception: when the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

No — do not report together. D89.42 carries an Excludes1 note covering D47.09: “other mast cell neoplasms of uncertain behavior (D47.09)”

Sole exception: when the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Side by side

D47.09Other mast cell neoplasms of uncertain behaviorD89.42Idiopathic mast cell activation syndrome
Billing statusBillableBillable
ClassificationC00-D49 — Neoplasms (C00-D49)D50-D89 — Diseases of the Blood and Blood-forming Organs and Certain Disorders Involving the Immune Mechanism (D50-D89)
DefinitionOther mast cell neoplasms of uncertain behavior is a billable ICD-10-CM diagnosis code (D47.09).Idiopathic mast cell activation syndrome is a billable ICD-10-CM diagnosis code (D89.42).
Includes
Extracutaneous mastocytoma
Mast cell tumor NOS
Mastocytoma NOS
Mastocytosis NOS
defects in the complement system
immunodeficiency disorders, except human immunodeficiency virus [HIV] disease
sarcoidosis
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Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources