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G10 ICD-10-CM Code: Huntington's disease

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FY 2026 Apr update / Diseases of the nervous system (G00-G99) / Systemic atrophies primarily affecting the central nervous system (G10-G14)

G10

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

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.

Buddy the Bee presenting code insight

Buddy Insight

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.

CMS-HCC V28

HCC 200

RAF 0.279

CMS-HCC V24

HCC 78

RAF 0.606

ACA/HHS

HCC 119

Varies by metal level

ESRD/PACE

HCC 78

RAF 0.079

RXHCC

HCC 160

RAF 3.223

Code Book Path

Official
G1Systemic atrophies primarily affecting the central nervous system (G10-G14)
G10Huntington's disease

Inclusion Terms

Official
  • Huntington's chorea
  • Huntington's dementia

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for G10 in this effective period.

Related Child Codes

Official

ICD-10-CM does not list child codes under G10 for this display context.

Includes

Official

ICD-10-CM does not list Includes notes for G10 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for G10 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for G10 in this effective period.

Use Additional

Official
  • 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)

Code Also

Official

ICD-10-CM does not list Code Also instructions for G10 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
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

MEAT Support

HCC Buddy guidance
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

Audit Caution

HCC Buddy guidance
Failing to code associated manifestations separately (dementia F02.80, depression F06.31, chorea) when documented
Confusing Huntington's chorea with other causes of chorea such as Sydenham's or tardive dyskinesia
Coding Huntington's based on family history alone without confirmed diagnosis in the patient
Not documenting the progressive nature and current disease stage for accurate severity capture

Common Mistakes

HCC Buddy guidance
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

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is G10 an HCC code?

Yes. G10 (Huntington's disease) 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), with a community non-dual aged RAF of 0.279. It is billable for payment year 2026.

Coder answer: G10 is billable and maps to V28 HCC 200, Friedreich and Other Hereditary Ataxias; Huntington Disease. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
G10
Description
Huntington's disease
HCC (V28)
HCC 200 — Friedreich and Other Hereditary Ataxias; Huntington Disease
RAF
0.279
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 200, Friedreich and Other Hereditary Ataxias; Huntington Disease
0.279
V24HCC 78, Parkinson's and Huntington's Diseases
0.606
ESRDHCC 78, Parkinson's and Huntington's Diseases
0.079
RxHCCHCC 160, Huntington's Disease
3.223

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. 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.

Work G10 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for G10

For G10 to 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.

Coder workflow notes

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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

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

Code Hierarchy

└G10Huntington's disease
└G10Huntington's disease

Because G10 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

G10 maps to CMS-HCC V28 category 200, Friedreich and Other Hereditary Ataxias; Huntington Disease. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. Because G10 carries a payment HCC, you can see what it adds to a RAF score and check the documentation the chart needs before it is submitted.

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