Q26.1 ICD-10-CM Code: Persistent left superior vena cava

Coder workflow for Q26.1

MedCoder structured workflow — derived from this code’s own official record

Before you code Q26.1

1. Laterality is coded in this family. Confirm the side documented — right, left, or bilateral — and select the matching code (this page’s code: left). The unspecified-side code applies only when the record states no side. Laterality is assigned from the documented side; where a bilateral code exists and both sides are documented, it is used instead of two unilateral codes (Guidelines I.B.13).

   See the relationships section · Guide: Laterality coding →

Choose the right path

1. Is the side documented?
   Yes → Select the code for the documented side (or the bilateral code when both sides are documented and one exists).
   No → Use the unspecified-side code only when the record states no side; a query is the alternative.

Consider Q26.1. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement

Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).

Laterality

Right, left or bilateral as documented; unspecified only when the record states no side (Guidelines I.B.13).

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Indexed Clinical Terms (2)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

• Malformation (congenital), great, vein, persistent left superior vena cava
• Persistence, persistent (congenital), left, superior vena cava

Don’t confuse Q26.1 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of Q26.1 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• Q26.4— Specificity relationship (Review)

  Overlapping diagnoses in the same category.

  Overlapping codes in the same category — the documentation decides which is the more specific fit.

  What moves you there: A record that documents no more than “Anomalous pulmonary venous connection, unspecified” takes Q26.4; specificity in the record moves it back here.

  Full comparison: Q26.1 vs Q26.4 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Verify Before Coding

• CC as a secondary diagnosis (FY2026). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name Q26.1 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 1 Excludes2 note: P29 — Cardiovascular disorders originating in the perinatal period (via Q26.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

Referenced by 2 Code Also instructions across 2 chapters: I27.21 — Secondary pulmonary arterial hypertension (via Q26.-), Z71.87 — Encounter for pediatric-to-adult transition counseling (via Q26.-).

These codes suggest coding this condition alongside when both are present.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: CC — Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 9 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 2 MS-DRGs: DRG 306 (MDC 05), DRG 307 (MDC 05).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):MAL001 — Cardiac and circulatory congenital anomalies (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as CC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

Q26.0 — Congenital stenosis of vena cava, Q26.8 — Other congenital malformations of great veins, Q27.30 — Arteriovenous malformation, site unspecified, Q27.4 — Congenital phlebectasia, Q28.0 — Arteriovenous malformation of precerebral vessels, Q28.1 — Other malformations of precerebral vessels, Q28.8 — Other specified congenital malformations of circulatory system, Q28.9 — Congenital malformation of circulatory system, unspecified

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Cardiac and circulatory congenital anomalies).

Q25.48 — Anomalous origin of subclavian artery, Q25.49 — Other congenital malformations of aorta, Q25.5 — Atresia of pulmonary artery, Q25.6 — Stenosis of pulmonary artery, Q25.71 — Coarctation of pulmonary artery, Q25.72 — Congenital pulmonary arteriovenous malformation, Q25.79 — Other congenital malformations of pulmonary artery, Q25.8 — Other congenital malformations of other great arteries, Q25.9 — Congenital malformation of great arteries, unspecified, Q26.0 — Congenital stenosis of vena cava, Q26.2 — Total anomalous pulmonary venous connection, Q26.3 — Partial anomalous pulmonary venous connection, Q26.4 — Anomalous pulmonary venous connection, unspecified, Q26.5 — Anomalous portal venous connection, Q26.6 — Portal vein-hepatic artery fistula, Q26.8 — Other congenital malformations of great veins, Q26.9 — Congenital malformation of great vein, unspecified, Q27.0 — Congenital absence and hypoplasia of umbilical artery, Q27.1 — Congenital renal artery stenosis, Q27.2 — Other congenital malformations of renal artery, +87 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Malformation”, “Persistence, persistent”; these codes share that main term but sit in a different category of the Tabular List.

Q25.45 — Double aortic arch (double aortic arch), Q25.46 — Tortuous aortic arch (convolutions, aortic arch), Q25.47 — Right aortic arch (right aortic arch), Q25.49 — Other congenital malformations of aorta (aorta, specified type NEC), Q25.5 — Atresia of pulmonary artery (pulmonary, artery, atresia), Q25.6 — Stenosis of pulmonary artery (pulmonary, artery, stenosis), Q25.72 — Congenital pulmonary arteriovenous malformation (pulmonary, arteriovenous), Q25.79 — Other congenital malformations of pulmonary artery (pulmonary, artery, specified type NEC), Q25.8 — Other congenital malformations of other great arteries (great, artery, specified type NEC), Q25.9 — Congenital malformation of great arteries, unspecified (great, artery), Q27.2 — Other congenital malformations of renal artery (renal artery), Q27.30 — Arteriovenous malformation, site unspecified (arteriovenous, aneurysmatic), Q27.31 — Arteriovenous malformation of vessel of upper limb (arteriovenous, aneurysmatic, peripheral, upper limb), Q27.32 — Arteriovenous malformation of vessel of lower limb (arteriovenous, aneurysmatic, peripheral, lower limb), Q27.33 — Arteriovenous malformation of digestive system vessel (arteriovenous, aneurysmatic, peripheral, digestive system, congenital), Q27.34 — Arteriovenous malformation of renal vessel (arteriovenous, aneurysmatic, peripheral, renal vessel), Q27.39 — Arteriovenous malformation, other site (arteriovenous, aneurysmatic, peripheral, other specified site), Q27.8 — Other specified congenital malformations of peripheral vascular system (peripheral vascular system, specified type NEC), Q27.9 — Congenital malformation of peripheral vascular system, unspecified (peripheral vascular system), Q28.0 — Arteriovenous malformation of precerebral vessels (arteriovenous, aneurysmatic, precerebral vessels), +181 more

Contextual Map

Every relationship of Q26.1 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run Q26.1 with these 3 related codes in Claim Check

Hierarchy

• Q00-QA1 — Chapter 17: Congenital Malformations, Deformations and Chromosomal Abnormalities (Q00-QA1) (Q00-QA1)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q20-Q28 — Congenital malformations of the circulatory system[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Referenced by Excludes2 notes

• P29 — Cardiovascular disorders originating in the perinatal period[Excludes2](via Q26.-): “congenital malformations of the circulatory system (Q20-Q28)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Code Also instructions

• I27.21 — Secondary pulmonary arterial hypertension[Code Also](via Q26.-): “congenital heart disease (Q20-Q28)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• Z71.87 — Encounter for pediatric-to-adult transition counseling[Code Also](via Q26.-): “congenital malformations of the circulatory system (Q20-Q28)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Clinical classification (CCSR)

• MAL001 — Cardiac and circulatory congenital anomalies[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

MS-DRG Grouper

• CC — Complication or Comorbidity [MS-DRG severity]: “As a secondary diagnosis this code can raise the stay's MS-DRG severity tier (CC).”— CMS MS-DRG Definitions Manual (Appendix C) · FY2026
• DRG 306 — CARDIAC CONGENITAL AND VALVULAR DISORDERS WITH MCC[MS-DRG]: “CARDIAC CONGENITAL AND VALVULAR DISORDERS WITH MCC (MDC 05)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 307 — CARDIAC CONGENITAL AND VALVULAR DISORDERS WITHOUT MCC[MS-DRG]: “CARDIAC CONGENITAL AND VALVULAR DISORDERS WITHOUT MCC (MDC 05)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

MDC crossing

• MDC 05 — Diseases and Disorders of the Circulatory System[MDC crossing]: “Diseases and Disorders of the Circulatory System — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 17,209 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

• Malformation (congenital), great, vein, persistent left superior vena cava[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Persistence, persistent (congenital), left, superior vena cava[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (9)

• Q26 — Congenital malformations of great veins[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q26.0 — Congenital stenosis of vena cava[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q26.2 — Total anomalous pulmonary venous connection[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q26.3 — Partial anomalous pulmonary venous connection[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q26.4 — Anomalous pulmonary venous connection, unspecified[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q26.5 — Anomalous portal venous connection[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q26.6 — Portal vein-hepatic artery fistula[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q26.8 — Other congenital malformations of great veins[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• and 1 more

Change history

• FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data

CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page

Inpatient payment groups Official source data

CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page

Change history and date-of-service validity Official source data

CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page

Comparisons, relationships and the contextual map MedCoder structured relationship

Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears

Summary and FAQ answers MedCoder explanation

Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Nearest Codes in This Family

Official ICD-10-CM classifications closest to Q26.1 in its code family, with their registry titles.

• Q26 — Congenital malformations of great veins
• Q26.0 — Congenital stenosis of vena cava
• Q26.2 — Total anomalous pulmonary venous connection
• Q26.3 — Partial anomalous pulmonary venous connection
• Q26.4 — Anomalous pulmonary venous connection, unspecified
• Q26.5 — Anomalous portal venous connection
• Q26.6 — Portal vein-hepatic artery fistula
• Q26.8 — Other congenital malformations of great veins
• Q26.9 — Congenital malformation of great vein, unspecified

View all codes in the Q26 family