2027 ICD-10-CM Diagnosis Code Q21.16Sinus venosus atrial septal defect, unspecified

ICD-10-CM Codes›Q00-Q99›Q20-Q28›Q21

ICD-10-CM Q21.16
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

Q21.16 is a billable ICD-10-CM diagnosis code for sinus venosus atrial septal defect, unspecified. 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 51 closely related codes. The code is exempt from POA reporting. Coders also document this condition as sinus venosus atrial septal defect. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cardiac and circulatory congenital anomalies.

Code Identity

ICD-10-CM Code
Q21.16
Billable Status
Yes — Valid for Submission
Code Describes
Sinus venosus atrial septal defect, unspecified
Short Description
Sinus venosus atrial septal defect, unspecified
Same as the full description in the CMS dataset.
Parent Code
Q21.1
Atrial septal defect

Code Classification

ChapterQ00-Q99Congenital malformations, deformations and chromosomal abnormalities
SectionQ20-Q28Congenital malformations of the circulatory system
CategoryQ21Congenital malformations of cardiac septa
This CodeQ21.16Sinus venosus atrial septal defect, unspecified

Present on Admission (POA)Billing

Q21.16 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).

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Sinus venosus atrial septal defect
  • Sinus venosus defect with overriding inferior vena cava
  • Sinus venosus defect with overriding superior vena cava

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Q21.16: its own notes plus those printed at Q21.1, 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.

  • Sinus venosus defect, 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 Q21.1 Atrial septal defect applies to 8 codes
  • ostium primum atrial septal defect (type I) (Q21.20)
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 Q21.16, its category, or a range that includes it.

Use Additional Code 1

These codes say to use an additional code from the note, and Q21.16 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 Q21.16 may also be needed to fully describe the condition. The note gives no sequencing direction.

  • I27.83 Eisenmenger's syndrome
    atrial septal defect (Q21.1-) names Q21.1-, which includes this code
  • Q87.85 MED13L syndrome
    congenital malformations of cardiac septa (Q21.-) names Q21.-, 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

  • Heart Septal Defects, Atrial

    developmental abnormalities in any portion of the atrial septum resulting in abnormal communications between the two upper chambers of the heart. classification of atrial septal defects is based on location of the communication and types of incomplete fusion of atrial septa with the endocardial cushions in the fetal heart. they include ostium primum, ostium secundum, sinus venosus, and coronary sinus defects.

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 Q21.16 replaces the following previously assigned code(s):

  • Q21.1 - Atrial 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 Q21.16Overview

What is the ICD-10 code for sinus venosus atrial septal defect, unspecified?

The ICD-10-CM code for sinus venosus atrial septal defect, unspecified is Q21.16 (sometimes written as Q2116). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is Q21.16 (Atrial septal defect) a billable code?

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

What MS-DRG does Q21.16 group to?

When sinus venosus atrial septal defect, unspecified 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 Q21.16 a CC or MCC?

CMS lists Q21.16 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 51 closely related codes in its exclusion list.

Is Q21.16 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 sinus venosus atrial septal defect, unspecified on inpatient claims. The code appears in the Congenital malformations of the circulatory system (Q20-Q28) range of the CMS exempt list.