Q21.9Congenital malformation of cardiac septum, unspecified

Q21.9 is the ICD-10-CM diagnosis code for congenital malformation of cardiac septum, unspecified. It belongs to category Q21 (congenital malformations of cardiac septa), block Q20-Q28 (congenital malformations of the circulatory system) and chapter 17 (congenital malformations, deformations, chromosomal abnormalities, and genetic disorders). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within Q21, choose Q21.9 (Congenital malformation of cardiac septum, unspecified) only when documentation doesn't support a more specific option: ventricular septal defect (Q21.0), atrial septal defect (Q21.1), atrioventricular septal defect (Q21.2), tetralogy of Fallot (Q21.3), Aortopulmonary septal defect (Q21.4) and other congenital malformations of cardiac septa (Q21.8).

It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.

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.

It is exempt from present-on-admission (POA) reporting, so no POA indicator is required.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as 745.9 (unspecified defect of septal closure).