ICD-10-CM 2027
ICD-10 code for endocardial cushion defect incomplete
From the official ICD-10-CM alphabetic index entry “Incomplete › endocardial cushion defect”. Page updated September 29, 2026.
About coding endocardial cushion defect incomplete
The ICD-10-CM code for endocardial cushion defect incomplete is Q21.21 (Partial atrioventricular septal defect).
Within Q21.2 (atrioventricular septal defect), Q21.21 is specifically for partial atrioventricular septal defect. Related codes cover unspecified as to partial or complete (Q21.20), Transitional atrioventricular septal defect (Q21.22) and complete atrioventricular septal defect (Q21.23).
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 306 (Cardiac Congenital and Valvular Disorders with MCC, relative weight 1.546) and DRG 307 (Cardiac Congenital and Valvular Disorders without MCC, relative weight 0.9148), in MDC 05 (Diseases and Disorders of the Circulatory System), 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 endocardial cushion defect incomplete ICD-10 codes
What is the ICD-10 code for endocardial cushion defect incomplete?
- Q21.21 — Partial atrioventricular septal defect.
Is Q21.21 billable?
- Yes. Q21.21 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can Q21.21 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict Q21.21 as a principal diagnosis.
Is Q21.21 a CC or MCC?
- Q21.21 is a CC (complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.