2027 ICD-10-CM Diagnosis Code Q21.23Complete atrioventricular septal defect

ICD-10-CM Codes›Q00-Q99›Q20-Q28›Q21

ICD-10-CM Q21.23
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

Q21.23 is a billable ICD-10-CM diagnosis code for complete atrioventricular septal defect. 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.

Q21.23 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
Q21.23
Billable Status
Yes — Valid for Submission
Code Describes
Complete atrioventricular septal defect
Short Description
Complete 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 CodeQ21.23Complete atrioventricular septal defect

Present on Admission (POA)Billing

Q21.23 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

Q21.23 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 common atrioventricular valve chordae tendinae
  • Abnormality of common atrioventricular valve in atrioventricular septal defect
  • Abnormality of common atrioventricular valve papillary muscle
  • Accessory tissue on common atrioventricular valve leaflet
  • Arcade abnormality of common atrioventricular valve chordae
  • Atrioventricular septal defect and common atrioventricular junction
  • Atrioventricular septal defect with common atrioventricular orifice
  • Atrioventricular septal defect, atrial and ventricular components with common atrioventricular valve with unbalanced commitment of valve to left ventricle
  • Atrioventricular septal defect, atrial and ventricular components with common atrioventricular valve with unbalanced commitment of valve to right ventricle
  • Atrioventricular septal defect: atrial and ventricular components
  • Common atrioventricular canal
  • Common atrioventricular junction
  • Common atrioventricular junction with spontaneous fibrous closure of atrioventricular septal defect
  • Common atrioventricular orifice in double inlet ventricle
  • Common atrioventricular valve chordae to outlet septum
  • Common atrioventricular valve chordae too long
  • Common atrioventricular valve chordae too short
  • Common atrioventricular valve prolapse
  • Common atrioventricular-type ventricular septal defect
  • Common atrium
  • Common atrium with common atrioventricular junction
  • Congenital cleft of cardiac valve
  • Double orifice of common atrioventricular valve
  • Endocardial cushion defect
  • Fused common atrioventricular valve papillary muscle
  • Hypoplasia of common atrioventricular valve
  • Hypoplastic common atrioventricular valve papillary muscle
  • Parachute malformation of common atrioventricular valve
  • Triple orifice of left ventricular component of common atrioventricular valve
  • True cleft of common atrioventricular valve leaflet

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Q21.23: 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.

  • Common atrioventricular canal
  • Common atrioventricular septal defect
  • Common endocardial cushion defect
  • Ostium primum atrial septal defect (type I) with common atrioventricular valve and a moderate or larger inlet VSD

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 Q21.23, its category, or a range that includes it.

Use Additional Code 1

These codes say to use an additional code from the note, and Q21.23 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 Q21.23 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 Q21.23 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 Q21.23Overview

What is the ICD-10 code for complete atrioventricular septal defect?

The ICD-10-CM code for complete atrioventricular septal defect is Q21.23 (sometimes written as Q2123). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is Q21.23 (Atrioventricular septal defect) a billable code?

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

What MS-DRG does Q21.23 group to?

When complete atrioventricular septal defect 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 Q21.23 a CC or MCC?

CMS lists Q21.23 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 Q21.23 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 complete atrioventricular septal defect on inpatient claims. The code appears in the Congenital malformations of the circulatory system (Q20-Q28) range of the CMS exempt list.

Does Q21.23 risk-adjust for Medicare Advantage payment?

Not for Medicare Advantage: Q21.23 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).