Q21 ICD-10-CM Code: Congenital malformations of cardiac septa
Q21 is not a CMS-HCC payment code. MEAT criteria · RAF Calculator · HCC coding software
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
Header CodeICD-10-CMOfficial ICD-10-CMCodebook guidanceCongenital malformations of cardiac septa
CMS-HCC V28
N/A—
Not mapped
CMS-HCC V24
N/A—
Not mapped
ACA/HHS
N/A—
Not mapped
ESRD/PACE
N/A—
Not mapped
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for Q21. Check the code and parent instructions in the Code Book.
Excludes 2
Official- inborn errors of metabolism (E70-E88)Inherited from Q00-QA0
Related Codes
Includes
OfficialNo Includes notes are included in this display for Q21. Check the code and parent instructions in the Code Book.
Excludes 1
Official- acquired cardiac septal defect (I51.0)
Code First
OfficialNo Code First sequencing instructions are included in this display for Q21. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for Q21. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for Q21. Check the code and parent instructions in the Code Book.
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 →
- Code
- Q21
- Description
- Congenital malformations of cardiac septa
- HCC (V28)
- No CMS-HCC V28 mapping
- RAF reference coefficient
- —
- Billable
- No
- Payment year
- 2026
Coder workflow notes
Get the V28 mapping + MEAT cheat sheet
One printable reference: check representative V28 mappings and the documentation reminders your note needs. Free, no card.
Free PDF. No card. Unsubscribe anytime.
What This Code Means
Q21 is the ICD-10-CM diagnosis code for congenital malformations of cardiac septa. Q21 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).
Header codes like Q21 cannot be reported on claims directly; they organize child codes that share clinical context. Coders should select the billable child code that matches the documented presentation and then verify its current source-backed HCC mapping. Do not infer a child code or risk adjustment value from the header alone.
HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for Q21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Excludes 1, Do NOT code together
- acquired cardiac septal defect (I51.0)