What does ICD-10-CM code G20.A1 mean?
G20.A1 represents Parkinson's disease without dyskinesia, without mention of fluctuations. This neurological condition is classified under Chapter 6 (Diseases of the Nervous System) and is commonly encountered in both inpatient and outpatient settings. Coders frequently reference this code as icd 10 parkinson disease or parkinson disease.
This is classified as a chronic condition requiring ongoing management and monitoring.
Code category and hierarchy
- Chapter: 6 – Diseases of the Nervous System (G00-G99)
- Category: G20
- Code: G20.A1 – Parkinson's disease without dyskinesia, without mention of fluctuations
Guideline notes and coding considerations
Important Guideline Note
Assign G20.A1 only when documentation clearly supports this diagnosis. Review the excludes notes and ensure no conflicts with other assigned codes.
- 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-)
Learn the underlying rules in the ICD-10 Coding Guidelines, Specificity Requirements, Risk Adjustment & MEAT Documentation.
Documentation tips (what coders should confirm)
- Verify the clinical documentation supports the use of G20.A1
- Use additional code: code, if applicable, to identify: | dementia with anxiety ( F02.84 , F02.A4, F02.B4, F02.C4) | dementia with behavioral
- This is a risk-adjusted diagnosis — ensure annual documentation with MEAT criteria (Monitor, Evaluate, Assess/Address, Treat)
- As a chronic condition, document current status and treatment at each encounter for risk adjustment
Validate G20.A1 Against ICD 10 CM Coding Guidelines
Check this code against official guidelines for conflicts and compliance issues.
Risk adjustment and HCC mapping
HCC Impact
G20.A1 (Parkinson's disease without dyskinesia, without mention of fluctuations) maps to the following HCC categories: CMS-HCC V24: HCC 78, CMS-HCC V28: HCC 199, RxHCC V08: HCC 161, ESRD V24: HCC 78. Proper documentation using MEAT criteria (Monitor, Evaluate, Assess/Address, Treat) is required for each encounter to support risk-adjusted diagnoses.
Learn more about risk adjustment documentation in our Risk Adjustment & MEAT Documentation Guide.
Related ICD-10 codes
Frequently Asked Questions
The ICD-10-CM code for icd 10 parkinson disease is G20.A1, which represents parkinson's disease without dyskinesia, without mention of fluctuations. This code is also commonly referenced as parkinson disease. Verify this code using the ICD Code Auditor to ensure guideline compliance.
Yes. G20.A1 is an active ICD-10-CM diagnosis code used to classify parkinson's disease without dyskinesia, without mention of fluctuations for clinical documentation, reporting, and medical billing purposes.
Use the ICD Code Auditor to check G20.A1 against official ICD-10-CM coding guidelines. The tool validates by fiscal year and patient gender to identify potential conflicts.
For risk adjustment purposes, G20.A1 (Parkinson's disease without dyskinesia, without mention of fluctuations) must be documented and assessed at least once per calendar year. The condition should be actively addressed during the encounter using MEAT criteria: Monitored, Evaluated, Assessed/Addressed, or Treated. Simply listing the condition in the problem list without clinical action does not satisfy documentation requirements.
Yes. G20.A1 maps to HCC 78 in the CMS-HCC V24 model, and HCC 199 in V28. Accurate coding of this condition directly impacts RAF scores for Medicare Advantage plans. Ensure documentation demonstrates the condition was evaluated and managed during the encounter.
Documentation should clearly describe the clinical condition represented by G20.A1 (Parkinson's disease without dyskinesia, without mention of fluctuations). Include relevant clinical findings, diagnostic test results, provider assessment, and the treatment plan. The diagnosis must be supported by the medical record and not based solely on lab results without clinical interpretation.
Sources
Reviewed by: Certified ICD-10 Coding & Risk Adjustment Specialist
Learn more about our Clinical Coding Review Process