ICD-10-CM 2027
ICD-10 code for secundum ostium
From the official ICD-10-CM alphabetic index entry “Ostium › secundum (arteriosum) (defect) (patent) (persistent)”. Page updated September 29, 2026.
About coding secundum ostium
The ICD-10-CM code for secundum ostium is Q21.11 (Secundum atrial septal defect).
Within Q21.1 (atrial septal defect), Q21.11 is specifically for secundum atrial septal defect. Related codes cover unspecified (Q21.10), Patent foramen ovale (Q21.12), coronary sinus atrial septal defect (Q21.13), superior sinus venosus atrial septal defect (Q21.14), inferior sinus venosus atrial septal defect (Q21.15), sinus venosus atrial septal defect, unspecified (Q21.16) and other specified atrial septal defect (Q21.19).
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 secundum ostium ICD-10 codes
What is the ICD-10 code for secundum ostium?
- Q21.11 — Secundum atrial septal defect.
Is Q21.11 billable?
- Yes. Q21.11 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can Q21.11 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict Q21.11 as a principal diagnosis.
Is Q21.11 a CC or MCC?
- Q21.11 is a CC (complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.