M08.1 ICD-10-CM Code: Juvenile ankylosing spondylitis
M08.1 maps to CMS-HCC V28 93 (RAF 0.617). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC Buddy coding tools
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Inflammatory polyarthropathies (M05-M14)
M08.1
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceJuvenile ankylosing spondylitis
A type of arthritis in children that primarily affects the spine and causes progressive stiffening and fusion of the vertebrae.
Buddy Insight
Juvenile ankylosing spondylitis represents a specific form of inflammatory spinal arthritis in children that primarily affects the axial skeleton and can lead to spinal fusion.
CMS-HCC V28
MappedHCC 93
RAF 0.617
CMS-HCC V24
MappedHCC 40
RAF 0.421
ACA/HHS
MappedHCC 56
Varies by metal level
ESRD/PACE
MappedHCC 40
RAF 0.058
RXHCC
MappedHCC 83
RAF 0.222
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for M08.1 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M08.1 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M08.1 in this effective period.
Excludes 1
Official- ankylosing spondylitis in adults (M45.0-)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M08.1 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M08.1 in this effective period.
Code Also
Official- any associated underlying condition, such as:
- regional enteritis [Crohn's disease] (K50.-)
- ulcerative colitis (K51.-)
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 M08.1 an HCC code?
Yes. M08.1 (Juvenile ankylosing spondylitis) maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under V24), with a community non-dual aged RAF of 0.617. It is billable for payment year 2026.
Coder answer: M08.1 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
- M08.1
- Description
- Juvenile ankylosing spondylitis
- HCC (V28)
- HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
- RAF
- 0.617
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
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 M08.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for M08.1
For M08.1 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 M08.1 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
M08.1 is the ICD-10-CM diagnosis code for juvenile ankylosing spondylitis. A type of arthritis in children that primarily affects the spine and causes progressive stiffening and fusion of the vertebrae. M08.1 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, M08.1 maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders (HCC 93) with a community, non-dual, aged base RAF weight of 0.617. Under the older CMS-HCC V24 model, M08.1 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 40) with a community, non-dual, aged base RAF weight of 0.421. 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.
This is the pediatric equivalent of ankylosing spondylitis and should only be used for patients under 18 years old. Because M08.1 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 M08.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is the pediatric equivalent of ankylosing spondylitis and should only be used for patients under 18 years old
- •Document spinal involvement and any systemic manifestations to support medical necessity
Clinical Significance
Juvenile ankylosing spondylitis represents a specific form of inflammatory spinal arthritis in children that primarily affects the axial skeleton and can lead to spinal fusion. This condition requires specialized rheumatologic care and monitoring for progressive spinal deformity and functional impairment.
Documentation Requirements
- ✓Physician diagnosis of juvenile ankylosing spondylitis
- ✓Age of onset documented as under 16 years
- ✓Evidence of inflammatory spinal disease with sacroiliitis
- ✓HLA-B27 testing results when performed
- ✓Imaging studies showing characteristic spinal changes
- ✓Assessment of spinal mobility and chest expansion
- ✓Treatment with anti-TNF therapy or other biologics
- ✓Ophthalmologic screening for uveitis
Excludes 1, Do NOT code together
- ankylosing spondylitis in adults (M45.0-)