ICD-10-CM · Spine

M45.A0

Non-radiographic axial spondyloarthritis (nr-axSpA) affecting the spine at an unspecified vertebral region — inflammatory sacroiliitis confirmed on MRI without corresponding plain-film radiographic changes.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 8
Region: Spine

Drawn from CDCAAPCCMSIcdcodes

Documentation tips

What should appear in the chart to support M45.A0.

Source · Editorial brief grounded in 5 cited references ↓

Record the specific spinal region(s) involved by name — cervical, thoracic, lumbar, etc. — so the site-specific M45.A1–A8 codes can be used instead of the unspecified M45.A0.
Document MRI findings explicitly: sacroiliitis without corresponding plain-radiograph structural changes is what clinically and legally separates nr-axSpA from ankylosing spondylitis (M45.x).
Note inflammatory back pain characteristics: age of onset under 45, duration >3 months, morning stiffness >30 minutes, improvement with exercise but not rest — these features support the diagnosis in the record.
Record HLA-B27 status and CRP/ESR results; positive HLA-B27 or elevated acute-phase reactants strengthen the clinical picture and reduce audit risk when radiographs are negative.
State explicitly that plain-film X-rays do NOT show sacroiliitis or structural damage — the absence of radiographic change is a required distinguishing criterion; without this, payers may reclassify as ankylosing spondylitis.
If BASDAI or ASDAS scoring was performed, include the score value in the note — this supports medical necessity for biologic therapy prior authorizations tied to this diagnosis.

Related CPT procedures

Procedure codes commonly billed with M45.A0. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

99213 $95.19

Established patient office or outpatient visit requiring 20–29 minutes of total time or low-complexity medical decision-making.

99214 $135.61

Office visit for an established patient requiring moderate-complexity medical decision making (MDM), or 30–39 minutes of total provider time on the date of service.

99215 $192.39

Highest-level office or outpatient E/M visit for an established patient, qualifying via high-complexity medical decision making or 40–54 minutes of total provider time on the date of service.

72148 $191.72

Non-contrast MRI of the lumbar spine used to evaluate disc pathology, spinal stenosis, nerve root compression, and other structural abnormalities without administration of contrast material.

72141 $190.72

MRI of the cervical spinal canal and its contents performed without contrast material.

72158 $318.31

MRI of the lumbar spinal canal and its contents performed first without contrast, then repeated after contrast administration for enhanced visualization.

72197 View procedure details

77080 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M45.A0 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

Using M45.A0 (unspecified site) when the provider has documented a specific spinal region — step up to M45.A1–A8; unspecified codes invite downcoding and audit scrutiny.
Confusing nr-axSpA (M45.A0) with ankylosing spondylitis (M45.0–M45.9) — if X-ray shows structural sacroiliitis, the correct category is M45.x, not M45.A; misclassification affects biologic authorization pathways.
Defaulting to a nonspecific low-back pain code (M54.5x) instead of M45.A0 when the provider has clearly documented nr-axSpA — inflammatory back pain with a specific diagnosis should always be coded to the specific condition.
Applying M45.A0 to juvenile patients — juvenile (ankylosing) spondylitis is Excluded1 and belongs under M08.1.
Coding M45.A0 alongside M02.3- (Reiter's disease arthropathy) — the Excludes1 note prohibits their simultaneous assignment.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M45.A0 applies when a provider has diagnosed non-radiographic axial spondyloarthritis and the documentation does not specify a distinct spinal region (cervical, thoracic, lumbar, etc.). The defining clinical feature is sacroiliitis visible on MRI in the absence of radiographic (X-ray) evidence of structural damage — the hallmark that separates nr-axSpA from ankylosing spondylitis (M45.x). Supporting findings typically include inflammatory back pain with morning stiffness, elevated CRP/ESR, and/or HLA-B27 positivity. BASDAI scoring ≥4 is commonly used clinically to gauge disease activity.

Use M45.A0 only when spinal site is genuinely unspecified or spans multiple regions without a dominant site. If the treating provider documents a specific spinal region, step up to M45.A1 (occipito-atlanto-axial), M45.A2 (cervical), M45.A3 (cervicothoracic), M45.A4 (thoracic), M45.A5 (thoracolumbar), M45.A6 (lumbar), M45.A7 (lumbosacral), or M45.A8 (sacral/sacrococcygeal). M45.A0 should never be a convenience default when region is documented.

Category M45 carries an Excludes1 for arthropathy in Reiter's disease (M02.3-) and juvenile ankylosing spondylitis (M08.1), and an Excludes2 for Behçet's disease (M35.2). Do not use M45.A0 for those conditions. Per ICD-10-CM Official Guidelines, code assignment is based on the provider's diagnostic statement — if the record says nr-axSpA, assign M45.A0 (or a site-specific sibling); you do not need to independently verify ASAS criteria.

Sibling codes

Other billable codes under M45.A (laterality / anatomic variants).

M45.A4

Non-radiographic axial spondyloarthritis of thoracic region

M45.A1

Non-radiographic axial spondyloarthritis occipt-atlan-ax rgn

M45.A7

Non-radiographic axial spondyloarthritis of lumbosacr region

M45.A5

Non-radiographic axial spondyloarthritis of thrclm region

M45.A8

Non-radiographic axial spondyloarthritis sacr/sacrocygl rgn

M45.A2

Non-radiographic axial spondyloarthritis of cervical region

M45.AB

Non-radiographic axial spondyloarthritis mult site in spine

M45.A6

Non-radiographic axial spondyloarthritis of lumbar region

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 5 cited references ↓

01What is the difference between M45.A0 and ankylosing spondylitis codes like M45.6?

M45.A0 (nr-axSpA) requires MRI sacroiliitis with NO radiographic (X-ray) structural damage. M45.6 and other M45.x codes for ankylosing spondylitis require radiographic evidence of sacroiliitis. If X-rays show structural changes, use M45.x, not M45.A0.

02When should I use M45.A0 versus M45.A6 (lumbar region)?

Use M45.A0 only when the provider's documentation does not identify a specific spinal region, or the condition spans multiple regions without a dominant site. If the note specifies lumbar involvement, use M45.A6. M45.A0 is not a shortcut — always code to the highest specificity the documentation supports.

03Does the provider need to document ASAS classification criteria for M45.A0 to be valid?

No. Per ICD-10-CM Official Guidelines Section I.B.19, code assignment is based on the provider's diagnostic statement. If the record states non-radiographic axial spondyloarthritis, assign M45.A0. You do not independently audit clinical criteria to validate the code.

04Can M45.A0 and a low-back pain code (M54.5x) be coded together?

Generally no. Low-back pain is a symptom integral to nr-axSpA. Per ICD-10-CM guidelines, symptoms that are integral to a disease process are not coded separately. Code M45.A0 alone unless the low-back pain has a distinct, separately documented etiology.

05Is HLA-B27 positivity required to assign M45.A0?

Not for coding purposes — the provider's diagnosis statement is sufficient. Clinically, HLA-B27 supports the diagnosis and is often required by payers for biologic therapy authorization, so documenting it strengthens the record even though it is not a coding prerequisite.

06What CPT procedures are commonly linked to encounters coded with M45.A0?

MRI of the sacroiliac joints and spine (72148, 72141, 72197) are the primary imaging procedures. Evaluation and management codes 99213–99215 cover rheumatology office visits. DEXA (77080) is relevant for monitoring bone density in long-standing inflammatory disease.

07Can M45.A0 be used for a pediatric patient with axial spondyloarthritis?

No. Juvenile ankylosing spondylitis is classified under M08.1, which is listed as an Excludes1 note under category M45. Use M08.1 for patients whose spondylitis onset was in childhood or adolescence.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

01CDC ICD-10-CM Tabular List 2026 (FY2026, effective Oct 1, 2025)
02
aapc.com
https://www.aapc.com/codes/icd-10-codes/M45.A0
03
aapc.com
https://www.aapc.com/codes/icd-10-codes/M45.A
04
cms.gov
https://www.cms.gov/files/document/fy-2025-icd-10-cm-coding-guidelines.pdf
05
icdcodes.ai
https://icdcodes.ai/diagnosis/spondyloarthritis/documentation

Mira AI Scribe

Mira's AI scribe captures the MRI-confirmed sacroiliitis finding, absence of plain-film radiographic changes, inflammatory back pain descriptors (morning stiffness duration, improvement with activity), HLA-B27 result, CRP/ESR values, and the specific spinal region(s) involved. That documentation prevents site-unspecified fallback to M45.A0 when a more precise sibling code is warranted, and it blocks payer reclassification of nr-axSpA as ankylosing spondylitis.

See how Mira captures M45.A0 documentation