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Q23.4 ICD-10-CM Code: Hypoplastic left heart syndrome

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Risk adjustment
RxHCC V08 category 191

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v44, Appendix B.

  • MS-DRG 306 — CARDIAC CONGENITAL AND VALVULAR DISORDERS WITH MCC (MDC 05)
  • MS-DRG 307 — CARDIAC CONGENITAL AND VALVULAR DISORDERS WITHOUT MCC (MDC 05)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Coder workflow for Q23.4

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

Before you code Q23.4

  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 Q23.4. 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

Documentation: The record documents the condition on one side only.

Coding question: Which code in this family applies?

Path: Select the sibling code for the documented side.

Reason: Laterality is assigned from the documented side; the unspecified-side code is for records that state no side (Guidelines I.B.13).

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.

Don’t confuse Q23.4 with…

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

The codes most likely to be picked instead of Q23.4 — 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.

  • Q23.9— 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 “Congenital malformation of aortic and mitral valves, unspecified” takes Q23.9; specificity in the record moves it back here.

    Full comparison: Q23.4 vs Q23.9 →

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.

Code Overview

Hypoplastic left heart syndrome is a billable ICD-10-CM diagnosis code (Q23.4).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (8)

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.

Verify Before Coding

  • MCC as a secondary diagnosis (FY2027). 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 Q23.4 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 2 Excludes1 notes: Q23.0 — Congenital stenosis of aortic valve, Q25.4 — Other congenital malformations of aorta.

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 2 Excludes2 notes across 2 chapters: I08 — Multiple valve diseases (via Q23.-), P29 — Cardiovascular disorders originating in the perinatal period (via Q23.-).

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

Referenced by 1 Use Additional Code instruction: Q87.88 — CTNNB1 syndrome (via Q23.-).

These codes instruct coders to additionally report this code when it applies.

Referenced by 2 Code Also instructions across 2 chapters: I27.21 — Secondary pulmonary arterial hypertension (via Q23.-), Z71.87 — Encounter for pediatric-to-adult transition counseling (via Q23.-).

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

MS-DRG Grouper Relationships (FY2027)

Potential MS-DRG participation — not a DRG assignment.

FY2027 MS-DRG: MCC — Major 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 68 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 MCC — 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.

Q20.9 — Congenital malformation of cardiac chambers and connections, unspecified, Q22.4 — Congenital tricuspid stenosis, Q22.5 — Ebstein's anomaly, Q22.6 — Hypoplastic right heart syndrome, Q22.8 — Other congenital malformations of tricuspid valve, Q22.9 — Congenital malformation of tricuspid valve, unspecified, Q23.0 — Congenital stenosis of aortic valve, Q23.1 — Congenital insufficiency of aortic valve, Q23.2 — Congenital mitral stenosis, Q23.3 — Congenital mitral insufficiency, Q23.81 — Bicuspid aortic valve, Q23.82 — Congenital mitral valve cleft leaflet, Q23.88 — Other congenital malformations of aortic and mitral valves, Q23.9 — Congenital malformation of aortic and mitral valves, unspecified, Q24.8 — Other specified congenital malformations of heart, Q24.9 — Congenital malformation of heart, unspecified, Q27.30 — Arteriovenous malformation, site unspecified, Q27.4 — Congenital phlebectasia, Q28.0 — Arteriovenous malformation of precerebral vessels, Q28.1 — Other malformations of precerebral vessels, +47 more

Same clinical category (CCSR)

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

Q22.3 — Other congenital malformations of pulmonary valve, Q22.4 — Congenital tricuspid stenosis, Q22.5 — Ebstein's anomaly, Q22.6 — Hypoplastic right heart syndrome, Q22.8 — Other congenital malformations of tricuspid valve, Q22.9 — Congenital malformation of tricuspid valve, unspecified, Q23.0 — Congenital stenosis of aortic valve, Q23.1 — Congenital insufficiency of aortic valve, Q23.2 — Congenital mitral stenosis, Q23.3 — Congenital mitral insufficiency, Q23.8 — Other congenital malformations of aortic and mitral valves, Q23.81 — Bicuspid aortic valve, Q23.82 — Congenital mitral valve cleft leaflet, Q23.88 — Other congenital malformations of aortic and mitral valves, Q23.9 — Congenital malformation of aortic and mitral valves, unspecified, Q24.0 — Dextrocardia, Q24.1 — Levocardia, Q24.2 — Cor triatriatum, Q24.3 — Pulmonary infundibular stenosis, Q24.4 — Congenital subaortic stenosis, +87 more

Same Index main term, other category

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

Q16.1 — Congenital absence, atresia and stricture of auditory canal (external) (ear canal), Q16.4 — Other congenital malformations of middle ear (ear, middle), Q16.9 — Congenital malformation of ear causing impairment of hearing, unspecified (auditory canal, causing impairment of hearing), Q17.2 — Microtia (ear), Q17.8 — Other specified congenital malformations of ear (eustachian tube), Q18.8 — Other specified congenital malformations of face and neck (face), Q22.0 — Pulmonary valve atresia (pulmonic), Q22.3 — Other congenital malformations of pulmonary valve (defective, congenital, valve, pulmonary), Q22.4 — Congenital tricuspid stenosis (tricuspid valve), Q22.6 — Hypoplastic right heart syndrome (right heart syndrome), Q24.5 — Malformation of coronary vessels (artery NEC, coronary), Q24.8 — Other specified congenital malformations of heart (heart), Q24.9 — Congenital malformation of heart, unspecified (imperfect, congenital, heart), Q25.21 — Interruption of aortic arch (aortic, arch), Q25.29 — Other atresia of aorta (aorta), Q25.42 — Hypoplasia of aorta (aorta, aortic), Q25.5 — Atresia of pulmonary artery (pulmonary), Q25.79 — Other congenital malformations of pulmonary artery (artery, pulmonary), Q26.2 — Total anomalous pulmonary venous connection (vein NEC, pulmonary, total), Q26.3 — Partial anomalous pulmonary venous connection (vein NEC, pulmonary, partial), +143 more

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Prothrombin Time Test and INR (PT/INR)

Contextual Map

Every relationship of Q23.4 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 Q23.4 with these 7 related codes in Claim Check

Hierarchy

Referenced by Excludes1 notes

Referenced by Excludes2 notes

Referenced by Use Additional Code instructions

  • Q87.88 — CTNNB1 syndrome[Use Additional Code](via Q23.-): “congenital heart malformations (Q20.0-Q24.9)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Code Also instructions

Clinical classification (CCSR)

MS-DRG Grouper

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. 15,708 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2027

Index entries

  • Atresia, atretic, aortic (orifice) (valve), congenital with hypoplasia of ascending aorta and defective development of left ventricle (with mitral stenosis)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Atresia, atretic, aortic (orifice) (valve), in hypoplastic left heart syndrome[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Atresia, atretic, mitral valve, in hypoplastic left heart syndrome[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Development, defective, congenital, left ventricle, in hypoplastic left heart syndrome[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Hypoplasia, hypoplastic, aorta, aortic, ascending, in hypoplastic left heart syndrome[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Hypoplasia, hypoplastic, aorta, aortic, valve, in hypoplastic left heart syndrome[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Hypoplasia, hypoplastic, left heart syndrome[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Syndrome, hypoplastic left-heart[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (10)

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 FY2027 tabular list, index and tables, effective October 1, 2026 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v44.0 (October 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 — v44 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

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "Q23.4 — Hypoplastic left heart syndrome." ICD-10-CM FY2027. https://medcoder.ai/icd10/code/q23.4-hypoplastic-left-heart-syndrome

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Hypoplastic left heart syndrome

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027, and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to Q23.4 in its code family, with their registry titles.

View all codes in the Q23 family