G10
BillableHuntington's disease
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G10 an HCC code?
Yes. G10 maps to Friedreich and Other Hereditary Ataxias; Huntington Disease under the CMS-HCC V28 risk adjustment model (and Parkinson's and Huntington's Diseases under V24).
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 G10
For G10to 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 G10 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G10 is the ICD-10-CM diagnosis code for huntington's disease. Huntington's disease is a progressive genetic disorder that causes involuntary movements, emotional problems, and loss of cognitive abilities, typically appearing in middle age. G10 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering systemic atrophies primarily affecting the central nervous system (g10-g14).
Under the CMS-HCC V28 risk adjustment model, G10 maps to Friedreich and Other Hereditary Ataxias; Huntington Disease (HCC 200) with a community, non-dual, aged base RAF weight of 0.279. Under the older CMS-HCC V24 model, G10 maps to Parkinson's and Huntington's Diseases (HCC 78) with a community, non-dual, aged base RAF weight of 0.606. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
Always verify family history documentation and age of onset to support the diagnosis. Because G10 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for G10 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Always verify family history documentation and age of onset to support the diagnosis
- •Code any associated manifestations separately (e.g., dementia, depression, chorea) if they are documented and clinically relevant
Clinical Significance
Huntington's disease is a devastating autosomal dominant neurodegenerative disorder with no cure, requiring extensive multidisciplinary care including neurology, psychiatry, rehabilitation, and eventually full-time skilled nursing. This diagnosis signals very high long-term healthcare costs and resource utilization due to progressive cognitive decline, chorea, and behavioral disturbances.
Documentation Requirements
- ✓Confirmed diagnosis via genetic testing (CAG repeat expansion) or strong clinical criteria
- ✓Family history consistent with autosomal dominant inheritance pattern
- ✓Age of symptom onset documented
- ✓Current stage of disease and functional status
- ✓Associated manifestations documented separately (dementia, depression, chorea, dysphagia)
- ✓Current treatment plan including medications and supportive therapies
Use Additional Code
- code, if applicable, to identify:
- dementia with anxiety (F02.84, F02.A4, F02.B4, F02.C4)
- dementia with behavioral disturbance (F02.81-, F02.A1-, F02.B1-, F02.C1-)
- dementia with mood disturbance (F02.83, F02.A3, F02.B3, F02.C3)
- dementia with psychotic disturbance (F02.82, F02.A2, F02.B2, F02.C2)
- dementia without behavioral disturbance (F02.80, F02.A0, F02.B0, F02.C0)
- mild neurocognitive disorder due to known physiological condition (F06.7-)
Commonly Confused Codes
- •G25.5 — Other chorea: for chorea from causes other than Huntington's disease
- •G31.09 — Other frontotemporal dementia: can mimic Huntington's behavioral variant but lacks genetic basis and chorea
- •G20.A1-G20.C — Parkinson's disease codes: different neurodegenerative process with different movement disorder pattern
- •F02.80 — Dementia in other diseases: used as additional code for Huntington's dementia manifestation