Q21.11 ICD-10-CM Code: Secundum atrial septal defect
HCC Buddy Code Card
Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.
FY 2026 Apr update / Congenital malformations, deformations and chromosomal abnormalities (Q00-QA0) / Congenital malformations of the circulatory system (Q20-Q28)
Q21.11
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceSecundum atrial septal defect
A hole in the middle portion of the wall between the two upper chambers of the heart, the most common type of atrial septal defect.
CMS-HCC V28
N/A—
Not mapped
CMS-HCC V24
N/A—
Not mapped
ACA/HHS
MappedHCC 139
Varies by metal level
ESRD/PACE
N/A—
Not mapped
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
Official- Fenestrated atrial septum
- Patent or persistent ostium secundum defect (type II)
Excludes 2
Official- ostium primum atrial septal defect (type I) (Q21.20)
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for Q21.11 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for Q21.11 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for Q21.11 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for Q21.11 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for Q21.11 in this effective period.
Buddy Documentation Tip
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is Q21.11 an HCC code?
No. Q21.11 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
- Code
- Q21.11
- Description
- Secundum atrial septal defect
- HCC (V28)
- No CMS-HCC V28 mapping
- RAF
- —
- Billable
- Yes
- Payment year
- 2026
Coder workflow notes
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This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
Q21.11 is the ICD-10-CM diagnosis code for secundum atrial septal defect. A hole in the middle portion of the wall between the two upper chambers of the heart, the most common type of atrial septal defect. Q21.11 sits in the ICD-10-CM chapter for congenital malformations, deformations and chromosomal abnormalities (q00-qa0), within the section covering congenital malformations of the circulatory system (q20-q28).
Q21.11 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
Secundum ASDs are the most frequently diagnosed type; ensure documentation specifies this location for accurate coding.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for Q21.11 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Secundum ASDs are the most frequently diagnosed type; ensure documentation specifies this location for accurate coding
- •Document any associated defects such as partial anomalous pulmonary venous return which may require additional codes