M08.99 ICD-10-CM Code: Juvenile arthritis, unspecified, multiple sites
M08.99 maps to CMS-HCC V28 93. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · free HCC coding tools
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Inflammatory polyarthropathies (M05-M14)
M08.99
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceJuvenile arthritis, unspecified, multiple sites
A type of arthritis that develops in children, affecting multiple joints throughout the body, where the specific cause is not identified.
Buddy Insight
Juvenile arthritis affecting multiple sites indicates a systemic inflammatory condition that can significantly impact a child's overall function, growth, and quality of life.
CMS-HCC V28
MappedHCC 93
Code-level coefficient reference
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 056
Code-level coefficient reference
ESRD/PACE
MappedHCC 40
Code-level coefficient reference
RXHCC
MappedHCC 83
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for M08.99 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M08.99 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M08.99 in this effective period.
Excludes 1
Official- juvenile rheumatoid arthritis, unspecified (M08.0-)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M08.99 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M08.99 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M08.99 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 M08.99 an HCC code?
Yes. M08.99 (Juvenile arthritis, unspecified, multiple sites) maps to HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.617. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: M08.99 is billable and maps to V28 HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- M08.99
- Description
- Juvenile arthritis, unspecified, multiple sites
- HCC (V28)
- HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
- RAF reference coefficient
- 0.617
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work M08.99 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT Criteria for M08.99
For M08.99 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 M08.99 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
M08.99 is the ICD-10-CM diagnosis code for juvenile arthritis, unspecified, multiple sites. A type of arthritis that develops in children, affecting multiple joints throughout the body, where the specific cause is not identified. M08.99 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering inflammatory polyarthropathies (m05-m14).
Under the CMS-HCC V28 risk adjustment model, M08.99 maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders (HCC 93) with a source-labeled community, non-dual, aged reference coefficient of 0.617. No V24 mapping is shown for M08.99; use the applicable model and payment year when reviewing the V28 mapping. 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. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Use this code only when juvenile arthritis affects multiple sites and the specific type cannot be determined. Because M08.99 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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, source-labeled coefficient references, and MEAT documentation criteria for M08.99 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when juvenile arthritis affects multiple sites and the specific type cannot be determined
- •Ensure documentation specifies that multiple joints are involved to justify this code selection
Clinical Significance
Juvenile arthritis affecting multiple sites indicates a systemic inflammatory condition that can significantly impact a child's overall function, growth, and quality of life. This diagnosis suggests more severe disease requiring comprehensive management and close monitoring for complications and disease progression.
Documentation Requirements
- ✓Patient age at onset (must be under 16 years old)
- ✓Evidence of chronic arthritis lasting at least 6 weeks
- ✓Documentation of involvement in multiple joint sites
- ✓Specific identification of affected joints when possible
- ✓Functional assessment and impact on daily activities
- ✓Laboratory studies (inflammatory markers, autoantibodies)
- ✓Current medications and treatment response
- ✓Comprehensive imaging studies of affected joints