2026 ICD-10-CM Diagnosis Code Q21.21Partial atrioventricular septal defect

ICD-10-CM Codes›Q00-Q99›Q20-Q28›Q21

ICD-10-CM Q21.21
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

Q21.21 is a billable ICD-10-CM diagnosis code for partial atrioventricular septal defect. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 306 through 307. The code is exempt from POA reporting. Coders also document this condition as atrial septal defect with endocardial cushion defect, partial type. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cardiac and circulatory congenital anomalies.

Code Identity

ICD-10-CM Code
Q21.21
Billable Status
Yes — Valid for Submission
Code Describes
Partial atrioventricular septal defect
Short Description
Partial atrioventricular septal defect
Same as the full description in the CMS dataset.
Parent Code
Q21.2
Atrioventricular septal defect

Code Classification

ChapterQ00-Q99Congenital malformations, deformations and chromosomal abnormalities
SectionQ20-Q28Congenital malformations of the circulatory system
CategoryQ21Congenital malformations of cardiac septa
This CodeQ21.21Partial atrioventricular septal defect

Present on Admission (POA)Billing

Q21.21 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Atrial septal defect with endocardial cushion defect, partial type
  • Endocardial cushion defect
  • Partial defect of atrioventricular canal

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Incomplete atrioventricular canal
  • Incomplete atrioventricular septal defect
  • Incomplete endocardial cushion defect
  • Ostium primum atrial septal defect (type I) with separate atrioventricular valves
  • Partial atrioventricular canal
  • Partial endocardial cushion defect

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Canal
      • atrioventricular
        • incomplete
    • Canal
      • atrioventricular
        • partial
    • Defect, defective
      • atrial septal
        • ostium primum type (type I)
          • with
            • separate atrioventricular valves
    • Defect, defective
      • atrioventricular
        • septal
          • incomplete
    • Defect, defective
      • atrioventricular
        • septal
          • partial
    • Defect, defective
      • cushion, endocardial
        • incomplete
    • Incomplete
      • atrioventricular
        • canal
    • Incomplete
      • atrioventricular
        • septal defect
    • Incomplete
      • endocardial cushion defect

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MAL001
Cardiac and circulatory congenital anomalies
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Congenital Heart Defects

Congenital heart defects (CHDs) are problems with the structure of the heart. "Congenital" means that that the problems are present at birth. These defects happen when a fetus's heart doesn't develop normally during pregnancy. Congenital heart defects are the most common type of birth defect.

The full article covers:

  • What are congenital heart defects?
  • What causes congenital heart defects?
  • Who is more likely to have a baby with a congenital heart defect?
  • What are the symptoms of congenital heart defects?
  • What other problems do congenital heart defects cause?
  • How are congenital heart defects diagnosed?
  • What are the treatments for congenital heart defects?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Code History & ChangesHistory

Replacement Q21.21 replaces the following previously assigned code(s):

  • Q21.2 - Atrioventricular septal defect
FY 2023AddedAdded to the ICD-10-CM code setEffective October 1, 2022.
FY 2024–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About Q21.21Overview

Is Q21.21 (Atrioventricular septal defect) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report partial atrioventricular septal defect on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does Q21.21 group to?

When partial atrioventricular septal defect is the principal diagnosis on an inpatient stay, it groups to MS-DRG 306, 307, with relative weights from 0.9132 to 1.5758 depending on complications. Higher weights mean higher Medicare reimbursement.

Is Q21.21 exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for partial atrioventricular septal defect on inpatient claims.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.