2027 ICD-10-CM Diagnosis Code Q21.20Atrioventricular septal defect, unspecified as to partial or complete

ICD-10-CM Codes›Q00-Q99›Q20-Q28›Q21

ICD-10-CM Q21.20
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

Q21.20 is a billable ICD-10-CM diagnosis code for atrioventricular septal defect, unspecified as to partial or complete. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 306 through 307. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 60 closely related codes. The code is exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cardiac and circulatory congenital anomalies.

Q21.20 does not risk-adjust for Medicare Advantage under the CMS-HCC V28 model. It still risk-adjusts in the RxHCC Part D (V08) category 191 for payment year 2027.

Code Identity

ICD-10-CM Code
Q21.20
Billable Status
Yes — Valid for Submission
Code Describes
Atrioventricular septal defect, unspecified as to partial or complete
Short Description
Atrioventricular septal defect, unsp as to part or complete
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 CodeQ21.20Atrioventricular septal defect, unspecified as to partial or complete

Present on Admission (POA)Billing

Q21.20 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Congenital malformations of the circulatory system (Q20-Q28).

Medicare Risk Adjustment (HCC)Billing

Q21.20 does not risk-adjust for Medicare Advantage under the CMS-HCC V28 model, but it maps to payment categories in the other CMS models shown below.

CMS-HCC V28 (Medicare Advantage Payment Model)
Not mapped
no payment category in the model that pays 100% of MA risk scores
Prior Model (CMS-HCC V24)
Not mapped under V24
this diagnosis newly risk-adjusts under the V28 model
Part D (RxHCC)
RxHCC 191 — Ventricular Septal Defect and Major Congenital Heart Disorders
also risk-adjusts in the Part D prescription drug model (V08)

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Abnormality of atrioventricular valve leaflet in atrioventricular septal defect
  • Atrioventricular septal defect - isolated atrial component
  • Atrioventricular septal defect - isolated ventricular component
  • Atrioventricular septal defect - ventricular component
  • Atrioventricular septal defect - ventricular component under inferior bridging leaflet
  • Atrioventricular septal defect - ventricular component under superior bridging leaflet
  • Atrioventricular septal defect associated with tetralogy of Fallot
  • Atrioventricular septal defect with additional muscular ventricular septal defect
  • Atrioventricular septal defect with atrial and ventricular components and separate atrioventricular valves
  • Atrioventricular septal defect with atrioventricular valve regurgitation
  • Atrioventricular septal defect with atrioventricular valve regurgitation through left inferior bridging leaflet lateral mural commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through left septal commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through left superior bridging leaflet lateral mural commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through right anterosuperior inferior mural commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through right anterosuperior superior bridging leaflet commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through right inferior bridging leaflet inferior mural commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through right septal commissure
  • Atrioventricular septal defect with balanced ventricles
  • Atrioventricular septal defect with restrictive ventricular component
  • Atrioventricular septal defect with separate atrioventricular orifices
  • Atrioventricular septal defect with ventricular component and interchordal shunting under inferior bridging leaflet
  • Atrioventricular septal defect with ventricular component and interchordal shunting under superior bridging leaflet
  • Atrioventricular septal defect with ventricular component and shunting under connecting tongue with separate orifices
  • Atrioventricular septal defect with ventricular component under free floating superior bridging leaflet and chords to papillary muscle at right ventricular free wall
  • Atrioventricular septal defect with ventricular component under inferior bridging leaflet with chords to crest ventricular septum
  • Atrioventricular septal defect with ventricular component under superior bridging leaflet with chords at crest ventricular septum
  • Atrioventricular septal defect with ventricular component under superior bridging leaflet with chords to papillary muscle on right ventricular side septum
  • Atrioventricular septal defect with ventricular component under superior bridging leaflet without chordal attachment to ventricular septal crest
  • Atrioventricular septal defect with ventricular imbalance
  • Atrioventricular septal defect with ventricular imbalance consisting of dominant left ventricle and hypoplastic right ventricle
  • Atrioventricular septal defect with ventricular imbalance consisting of dominant right ventricle and hypoplastic left ventricle
  • Atrioventricular septal defect, blepharophimosis, radial and anal defect syndrome
  • Atrioventricular septal defect: atrial and ventricular components
  • Common atrioventricular canal
  • Common atrioventricular-type ventricular septal defect
  • Common atrium
  • Congenital abnormality of atrioventricular valve leaflet in atrioventricular septal defect
  • Congenital abnormality of atrioventricular valve papillary muscle in atrioventricular septal defect
  • Congenital abnormality of atrioventricular valves in atrioventricular septal defect
  • Congenital atrioventricular septal defect
  • Deficiency of atrioventricular valve leaflet in atrioventricular septal defect
  • Endocardial cushion defect
  • Fenestration of atrioventricular valve leaflet in atrioventricular septal defect
  • Flail atrioventricular valve leaflet in atrioventricular septal defect
  • Gelatinous atrioventricular valve leaflet in atrioventricular septal defect
  • Mass associated with atrioventricular valve leaflet in atrioventricular septal defect
  • Noncoapting atrioventricular valve leaflet in atrioventricular septal defect
  • Ostium primum defect
  • Residual interatrial communication
  • Spontaneous closure of atrial component of atrioventricular septal defect
  • Spontaneous closure of ventricular component of atrioventricular septal defect
  • Spontaneous closure of ventricular septal defect
  • Spontaneous closure of ventricular septal defect due to accessory tissue of atrioventricular valve
  • Thickened atrioventricular valve leaflet in atrioventricular septal defect
  • Ventricular imbalance

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Q21.20: its own notes plus those printed at Q21 and Chapter 17. A note printed at a category, block or chapter applies to every code under it.

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Atrioventricular canal, NOS
  • Endocardial cushion defect NOS
  • Ostium primum atrial septal defect (type I) NOS

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From Q21 Congenital malformations of cardiac septa applies to 17 codes
  • acquired cardiac septal defect (I51.0)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 17 (Q00-QA1) Congenital malformations, deformations and chromosomal abnormalities applies to 900 codes
  • inborn errors of metabolism (E70-E88)

Notes

General instructions on how these codes are used.

From Chapter 17 (Q00-QA1) Congenital malformations, deformations and chromosomal abnormalities applies to 900 codes
  • Codes from this chapter are not for use on maternal records

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name Q21.20, its category, or a range that includes it.

Excludes2 1

These codes carry an Excludes2 note naming Q21.20: its condition is not part of those codes, and both may be reported when the patient has both.

  • Q21.1 Atrial septal defect
    ostium primum atrial septal defect (type I) (Q21.20)

Use Additional Code 1

These codes say to use an additional code from the note, and Q21.20 is one of the codes named.

  • Q87.88 CTNNB1 syndrome
    congenital heart malformations (Q20.0-Q24.9) names Q20.0-Q24.9, which includes this code

Code Also 2

These codes say Q21.20 may also be needed to fully describe the condition. The note gives no sequencing direction.

  • Q87.85 MED13L syndrome
    congenital malformations of cardiac septa (Q21.-) names Q21.-, which includes this code
  • Q90 Down syndrome
    associated physical condition(s), such as atrioventricular septal defect (Q21.2-) names Q21.2-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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

Clinical InformationClinical

  • Atrioventricular Septal Defect

    a congenital heart malformation characterized by abnormalities in the anatomic structures that relate to the endocardial cushions. these abnormalities can include defects in the lower part of the atrial septum and the ventricular septum and lack of separation of the mitral and tricuspid valves.

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 Q21.20 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 2024–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About Q21.20Overview

What is the ICD-10 code for atrioventricular septal defect, unspecified as to partial or complete?

The ICD-10-CM code for atrioventricular septal defect, unspecified as to partial or complete is Q21.20 (sometimes written as Q2120). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is Q21.20 (Atrioventricular septal defect) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report atrioventricular septal defect, unspecified as to partial or complete on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does Q21.20 group to?

When atrioventricular septal defect, unspecified as to partial or complete is the principal diagnosis on an inpatient stay, it groups to MS-DRG 306, 307, with relative weights from 0.9146 to 1.5457 depending on complications. Higher weights mean higher Medicare reimbursement.

Is Q21.20 a CC or MCC?

CMS lists Q21.20 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 60 closely related codes in its exclusion list.

Is Q21.20 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 atrioventricular septal defect, unspecified as to partial or complete on inpatient claims. The code appears in the Congenital malformations of the circulatory system (Q20-Q28) range of the CMS exempt list.

Does Q21.20 risk-adjust for Medicare Advantage payment?

Not for Medicare Advantage: Q21.20 maps to no category in the CMS-HCC V28 model. It still risk-adjusts in the RxHCC Part D (V08) category 191 (Ventricular Septal Defect and Major Congenital Heart Disorders).