M45.A0
BillableNon-radiographic axial spondyloarthritis of unspecified sites in spine
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M45.A0 an HCC code?
Yes. M45.A0 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. 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.
MEAT Criteria for M45.A0
For M45.A0to 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 M45.A0 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M45.A0 is the ICD-10-CM diagnosis code for non-radiographic axial spondyloarthritis of unspecified sites in spine. An inflammatory spinal condition similar to ankylosing spondylitis but without the characteristic bone changes visible on X-rays, affecting unspecified areas of the spine. M45.A0 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering spondylopathies (m45-m49).
Under the CMS-HCC V28 risk adjustment model, M45.A0 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 93) with a community, non-dual, aged base RAF weight of 0.175. Under the older V24 model, M45.A0 mapped to the same category but with a base RAF weight of 0.307 — V28 recalibrated weights across the entire model. 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.
Non-radiographic axial spondyloarthritis is diagnosed by clinical and laboratory findings without radiographic evidence of fusion. Because M45.A0 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 M45.A0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Non-radiographic axial spondyloarthritis is diagnosed by clinical and laboratory findings without radiographic evidence of fusion
- •Ensure imaging has been reviewed and does not show typical ankylosing spondylitis changes before assigning this code
Clinical Significance
Non-radiographic axial spondyloarthritis represents early-stage disease before structural changes appear on conventional X-rays, requiring MRI or advanced imaging for diagnosis. Early recognition and treatment can prevent progression to radiographic ankylosing spondylitis.
Documentation Requirements
- ✓MRI evidence of sacroiliac joint inflammation without radiographic changes
- ✓Clinical criteria for axial spondyloarthritis met
- ✓Inflammatory back pain characteristics
- ✓HLA-B27 status and other laboratory markers
- ✓Response to NSAIDs documented
- ✓Assessment of disease activity using ASDAS or BASDAI
- ✓Exclusion of mechanical causes of back pain
- ✓Documentation of any peripheral manifestations
Commonly Confused Codes
- •M45.9 — Radiographic ankylosing spondylitis when structural changes present
- •M46.90 — Unspecified inflammatory spondylopathy without axial features
- •M54.5 — Low back pain without inflammatory characteristics
- •M53.9 — Dorsopathy when inflammatory component is established
- •M07.60 — Enteropathic arthropathies when IBD is primary diagnosis