G20.A1
BillableParkinson's disease without dyskinesia, without mention of fluctuations
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G20.A1 an HCC code?
Yes. G20.A1 maps to Parkinson and Huntington Diseases 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 G20.A1
For G20.A1 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 G20.A1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G20.A1 is the ICD-10-CM diagnosis code for parkinson's disease without dyskinesia, without mention of fluctuations. Parkinson's disease without involuntary movements (dyskinesia) and without motor fluctuations, a progressive neurological disorder affecting movement and muscle control. G20.A1 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering extrapyramidal and movement disorders (g20-g26).
Under the CMS-HCC V28 risk adjustment model, G20.A1 maps to Parkinson and Huntington Diseases (HCC 199) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, G20.A1 maps to Parkinson's and Huntington's Diseases (HCC 78) with a community, non-dual, aged base RAF weight of 0.584. 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.
Use this code when dyskinesia and fluctuations are explicitly documented as absent. Because G20.A1 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 G20.A1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code when dyskinesia and fluctuations are explicitly documented as absent
- •Distinguish between A1 (no fluctuations) and A2 (with fluctuations) based on clinical documentation
Clinical Significance
Parkinson's disease without dyskinesia and without fluctuations represents the earliest or most well-controlled stage of the disease, where motor symptoms respond consistently to medication without complications. This specific code captures treatment response status, which is essential for accurate risk stratification and tracking disease progression over time.
Documentation Requirements
- ✓Confirmed diagnosis of Parkinson's disease (not parkinsonism or secondary causes)
- ✓Explicit documentation that dyskinesia is absent
- ✓Explicit documentation that motor fluctuations are absent
- ✓Current medication regimen (levodopa, dopamine agonists, etc.)
- ✓Motor examination findings (bradykinesia, rigidity, tremor)
- ✓Functional status and disease stage if documented