Q26.9
BillableCongenital malformation of great vein, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is Q26.9 an HCC code?
No. Q26.9 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 Q26.9
For Q26.9to 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 Q26.9 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
Q26.9 is the ICD-10-CM diagnosis code for congenital malformation of great vein, unspecified. A birth defect affecting the large veins that return blood to the heart, where the specific type is not identified. Q26.9 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).
Q26.9 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 represents a congenital venous condition that may require cardiac monitoring and intervention. The zero RAF weight suggests minimal impact despite potential for complex care needs.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for Q26.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
Clinical Significance
Unspecified congenital great vein malformation indicates the presence of a venous anomaly affecting major vessels but lacks specific anatomic characterization. While less precise, this still represents a potentially significant cardiac condition requiring appropriate evaluation and management.
Documentation Requirements
- ✓Evidence of congenital venous malformation
- ✓Clinical signs and symptoms related to venous anomaly
- ✓Imaging studies attempting to characterize the defect
- ✓Hemodynamic impact assessment
- ✓Associated cardiac conditions evaluation
- ✓Reason why specific type cannot be determined
- ✓Management approach despite incomplete characterization
- ✓Cardiology consultation and follow-up plans
Commonly Confused Codes
- •Q26.0 — Congenital stenosis of vena cava (specific stenosis documented)
- •Q26.8 — Other congenital malformations of great veins (specific but atypical type)
- •I87.9 — Disorder of vein, unspecified (acquired venous condition)
- •Q27.9 — Congenital malformation of peripheral vascular system, unspecified (peripheral vessels)