Q26.1
BillablePersistent left superior vena cava
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is Q26.1 an HCC code?
No. Q26.1 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for Q26.1
For Q26.1to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed Q26.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
Q26.1 is the ICD-10-CM diagnosis code for persistent left superior vena cava. A birth defect where an extra vein (left superior vena cava) that normally disappears before birth persists, creating an abnormal pathway for blood return to the heart. Q26.1 sits in the ICD-10-CM chapter for congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (q00-qa0), within the section covering congenital malformations of the circulatory system (q20-q28).
Q26.1 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
This code maps to HCC 191 (Obesity) in the RxHCC model with RAF 0.0, which appears to be an incorrect mapping as this is a congenital venous anomaly. The zero RAF weight reflects the typically benign nature but may not account for associated complex cardiac conditions.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for Q26.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is often an incidental finding discovered during imaging for other reasons
- •Document whether the right superior vena cava is present or absent, as this affects clinical significance
Clinical Significance
Persistent left superior vena cava is typically a benign congenital variant but can be associated with other cardiac anomalies and may complicate certain medical procedures. Recognition is important for procedural planning and assessment of associated conditions.
Documentation Requirements
- ✓Echocardiographic or CT imaging confirmation
- ✓Documentation of drainage pattern (coronary sinus vs left atrium)
- ✓Assessment for associated cardiac anomalies
- ✓Right superior vena cava presence or absence
- ✓Clinical significance and hemodynamic impact
- ✓Procedural implications for cardiac interventions
- ✓Genetic counseling if part of syndrome
- ✓Follow-up recommendations based on associated findings
Commonly Confused Codes
- •Q26.2 — Total anomalous pulmonary venous connection (different venous anomaly)
- •Q26.8 — Other congenital malformations of great veins (less specific)
- •Q21.1 — Atrial septal defect (commonly associated but different defect)
- •Q26.9 — Congenital malformation of great vein, unspecified (not specific enough)