2026 ICD-10-CM Diagnosis Code M45.A4Non-radiographic axial spondyloarthritis of thoracic region
ICD-10-CM Codes›M00–M99›M45-M49›M45
- Billable — Valid for Submission
- Risk Adjusts — HCC 93
- Chronic Condition
M45.A4 is a billable ICD-10-CM diagnosis code for non-radiographic axial spondyloarthritis of thoracic region. 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 non-radiographic axial spondyloarthritis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Rheumatoid arthritis and related disease and Spondylopathies/spondyloarthropathy (including infective).
For Medicare Advantage risk adjustment, M45.A4 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
M45.A4 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.
- Non-radiographic axial spondyloarthritis
- Non-radiographic axial spondyloarthritis of lumbar region
- Non-radiographic axial spondyloarthritis of thoracic and lumbar regions
Index to Diseases and InjuriesGuidance
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.
Code History & ChangesHistory
Replacement M45.A4 replaces the following previously assigned code(s):
- M45.4 - Ankylosing spondylitis of thoracic region
Questions About M45.A4Overview
What is the ICD-10 code for non-radiographic axial spondyloarthritis of thoracic region?
The ICD-10-CM code for non-radiographic axial spondyloarthritis of thoracic region is M45.A4 (sometimes written as M45A4). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is M45.A4 (Non-radiographic axial spondyloarthritis) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report non-radiographic axial spondyloarthritis of thoracic region on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does M45.A4 group to?
When non-radiographic axial spondyloarthritis of thoracic region 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 HCC is M45.A4?
M45.A4 (non-radiographic axial spondyloarthritis of thoracic region) 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 M45.A4 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, M45.A4 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.
