2026 ICD-10-CM Diagnosis Code M08.1Juvenile ankylosing spondylitis
ICD-10-CM Codes›M00–M99›M05-M14›M08
- Billable — Valid for Submission
- Risk Adjusts — HCC 93
- Chronic Condition
M08.1 is a billable ICD-10-CM diagnosis code for juvenile ankylosing spondylitis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 545 through 547. Coders also document this condition as ankylosing spondylitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Juvenile arthritis and Spondylopathies/spondyloarthropathy (including infective).
For Medicare Advantage risk adjustment, M08.1 maps to CMS-HCC Category 93 (Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders) under the V28 model, adding a risk factor of about 0.617 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
M08.1 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Ankylosing spondylitis
- Ankylosing spondylitis with multisystem involvement
- Ankylosing spondylitis with organ / system involvement
- Juvenile ankylosing spondylitis
- Juvenile spondyloarthropathy
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Type 1 Excludes
- ankylosing spondylitis in adults M45.0
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Spondylitis (chronic) See Also: Spondylopathy, inflammatory;
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Ankylosing Spondylitis
Ankylosing spondylitis (AS) is a type of arthritis of the spine. It causes inflammation (swelling) between your vertebrae (the bones that make up your spine) and the joints between your spine and pelvis. AS inflammation can cause stiffness and make it difficult to move and bend.
The full article covers:
- What is ankylosing spondylitis?
- Who is more likely to get ankylosing spondylitis?
- What causes ankylosing spondylitis?
- What are the symptoms of ankylosing spondylitis?
- How is ankylosing spondylitis diagnosed?
- What are the treatments for ankylosing spondylitis?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert M08.1 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About M08.1Overview
What is the ICD-10 code for juvenile ankylosing spondylitis?
The ICD-10-CM code for juvenile ankylosing spondylitis is M08.1 (sometimes written as M081). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is M08.1 (Juvenile arthritis) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report juvenile ankylosing spondylitis on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does M08.1 group to?
When juvenile ankylosing spondylitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 545, 546, 547, with relative weights from 0.8362 to 2.4817 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of M08.1?
Under the General Equivalence Mappings, juvenile ankylosing spondylitis converts to ICD-9-CM 720.0 (ankylosing spondylitis). The mapping is approximate, so confirm the match fits the documentation.
What HCC is M08.1?
M08.1 (juvenile ankylosing spondylitis) maps to CMS-HCC Category 93 (Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders), commonly written as HCC 93, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 40 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 83.
Does M08.1 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, M08.1 adds a risk adjustment factor of about 0.617 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.288 to 0.617 depending on the payment segment). HCC 93 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 93 category page.
