M12.4 vs M25.4

M12.4 (Intermittent hydrarthrosis) compared with M25.4 (Effusion of joint), from the official CMS tabular data. Do not report these codes together: the official tabular list marks them Excludes1.

Can these codes be reported together?

No — do not report together. M25.4 carries an Excludes1 note covering M12.4: “intermittent hydrarthrosis (M12.4-)”

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

	M12.4Intermittent hydrarthrosis	M25.4Effusion of joint
Billing status	Non-billable header Report instead: M12.40, M12.411, M12.412, M12.419, M12.421	Non-billable header Report instead: M25.40, M25.411, M25.412, M25.419, M25.421
Classification	M00-M99 — Diseases of the Musculoskeletal System and Connective Tissue (M00-M99)	M00-M99 — Diseases of the Musculoskeletal System and Connective Tissue (M00-M99)
Definition	Intermittent hydrarthrosis is a non-billable ICD-10-CM category code (M12.4).	Effusion of joint is a non-billable ICD-10-CM category code (M25.4).

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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