ICD-10-CM · Spine

M45.AB

Non-radiographic axial spondyloarthritis (nr-axSpA) involving two or more distinct spinal regions simultaneously, where active spinal inflammation is confirmed but without the structural sacroiliac joint damage visible on plain radiographs.

Verified May 8, 2026 · 7 sources ↓

Status: Billable
Chapter: 13
Related CPT: 10
Region: Spine

Drawn from CDCicd10data.com 2026UCBAHASpondylitis Association

Documentation tips

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

Source · Editorial brief grounded in 7 cited references ↓

Name each affected spinal region explicitly (e.g., 'lumbar and thoracic regions') — 'multiple levels' alone may not justify M45.AB over M45.A0 on audit.
Record that radiographic sacroiliac joint changes are absent or do not meet modified New York criteria; this is the defining feature separating nr-axSpA from ankylosing spondylitis.
Document MRI findings (bone marrow edema, enthesitis) and/or inflammatory markers (CRP, ESR) and HLA-B27 status that support the nr-axSpA diagnosis in lieu of x-ray structural damage.
Specify whether the clinical picture is consistent with active inflammatory back pain — duration, morning stiffness, response to NSAIDs — to support medical necessity for biologics if prescribed.
If Behçet's disease is also present and separately documented, you may code M35.2 alongside M45.AB per the Excludes2 instruction at M45.

Related CPT procedures

Procedure codes commonly billed with M45.AB. 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.

72100 $40.42

Radiologic examination of the lumbosacral spine capturing two or three views, used to evaluate the lumbar vertebrae and sacrum for injury, degeneration, or structural abnormality.

72110 $53.44

Radiologic examination of the lumbar spine (lumbosacral) with a minimum of four views, including oblique and/or bending views.

86200 View procedure details

86235 View procedure details

Common coding pitfalls

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

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

Assigning M45.AB when only one spinal region is documented — single-region involvement requires a site-specific code (M45.A1–M45.A8), not the multi-site code.
Using M45.AB interchangeably with ankylosing spondylitis codes (M45.0–M45.9) — AS requires radiographic sacroiliac joint damage meeting modified New York criteria; nr-axSpA does not.
Defaulting to M45.A0 (unspecified sites) when the record actually names multiple regions — specificity is auditable and affects downstream research registries and payer edits.
Ignoring the Excludes1 note and coding M45.AB alongside M02.3- or M08.1 — these combinations are invalid; use only one category.
Applying a 7th-character extension to M45.AB — M-codes in this category do not use 7th-character trauma extensions (A/D/S).

Clinical context

Source · Editorial summary grounded in 7 cited references ↓

M45.AB is the site-specific code for nr-axSpA when the treating rheumatologist documents involvement at multiple spinal levels — for example, both lumbar and thoracic regions — in the absence of definitive radiographic sacroiliac joint changes. Use it only when the note explicitly names more than one spinal region; if only a single region is documented, select the appropriate single-site code from M45.A1–M45.A8. If spinal region involvement is not specified at all, default to M45.A0 (unspecified sites).

Nr-axSpA sits within category M45 (Ankylosing Spondylitis) but is clinically distinct: inflammation is present — often confirmed by MRI or elevated CRP/ESR plus HLA-B27 positivity — yet x-ray findings do not meet modified New York criteria for ankylosing spondylitis. The category M45.A subcodes were introduced effective October 1, 2021 (FY2022), specifically to capture this population and separate them from both AS (M45.0–M45.9) and unspecified spondylopathies.

Excludes1 at the M45 level bars simultaneous use of M45.AB with M02.3- (arthropathy in Reiter's disease) and M08.1 (juvenile ankylosing spondylitis) — these are mutually exclusive. Behçet's disease (M35.2) is an Excludes2 note, meaning it can be coded alongside M45.AB when both conditions are genuinely present and documented. M45.AB groups into MS-DRG v43.0 clusters 545–547 (Connective Tissue Disorders with/without CC/MCC).

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.A0

Non-radiographic axial spondyloarthritis unsp site in spin

M45.A2

Non-radiographic axial spondyloarthritis of cervical region

M45.A6

Non-radiographic axial spondyloarthritis of lumbar region

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 7 cited references ↓

01What is the difference between M45.AB and ankylosing spondylitis codes like M45.2 or M45.6?

Ankylosing spondylitis codes (M45.0–M45.9) require radiographic sacroiliac joint damage meeting modified New York criteria. M45.AB applies when spinal inflammation is present at multiple levels but x-rays do not show that structural SI joint damage — the 'non-radiographic' qualifier is the clinical and coding distinction.

02When should I use M45.A0 instead of M45.AB?

Use M45.A0 when the documentation does not specify which spinal region(s) are involved. If the provider names two or more distinct regions (e.g., cervical and lumbar), M45.AB is the correct, more specific code.

03Can M45.AB be coded with Behçet's disease (M35.2)?

Yes. The M45 category places M35.2 under an Excludes2 note, meaning both conditions can be coded together when each is independently documented and clinically present.

04How long has M45.AB been in the ICD-10-CM code set?

M45.AB was introduced as a new code effective October 1, 2021 (FY2022 ICD-10-CM). It remains valid and unchanged through FY2026 (effective October 1, 2025).

05Does M45.AB require a 7th character?

No. M45.AB is a complete billable code with no 7th-character extension. The A/D/S trauma extensions apply to injury S-codes, not M-category spondylopathy codes.

06What imaging supports the use of M45.AB over a non-specific inflammatory back pain code?

MRI demonstrating bone marrow edema or enthesitis at multiple spinal levels supports M45.AB. Normal or equivocal plain x-rays of the SI joints are expected — that is the defining 'non-radiographic' feature. Document the MRI findings, the spinal regions involved, and the clinical rationale for the nr-axSpA diagnosis.

07Can M45.AB be used as a primary diagnosis for biologic drug authorization?

M45.AB is the appropriate primary diagnosis code for nr-axSpA prior authorization requests for approved biologics. Payers vary in their system updates for this code; verify that the payer's system recognizes M45.A subcategory codes before submission, as noted in UCB's 2022 guidance.

Sources & references

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

01CDC ICD-10-CM Tabular List 2026 — https://www.cdc.gov/nchs/icd/icd-10-cm.htm
02icd10data.com 2026 ICD-10-CM M45.AB — https://www.icd10data.com/ICD10CM/Codes/M00-M99/M45-M49/M45-/M45.AB
03UCB USA nr-axSpA ICD-10 Code Reference (September 2022) — https://www.ucb-usa.com/sites/default/files/2023-11/nr-axspa-icd-10.pdf
04AHA Coding Clinic for ICD-10-CM: Non-Radiographic Axial Spondyloarthritis — https://www.findacode.com/newsletters/aha-coding-clinic/icd/non-radiographic-axial-spondyloarthritis-I084020.html
05Spondylitis Association of America — nr-axSpA Overview — https://spondylitis.org/about-spondylitis/overview-of-spondyloarthritis/non-radiographic-axial-spondyloarthritis-nr-axspa/
06Robinson PC, Siebert S. Nr-axSpA: Advances in Classification, Imaging and Therapy. PMC6514020 — https://pmc.ncbi.nlm.nih.gov/articles/PMC6514020/
07CMS ICD-10-CM FY2022 New Codes — https://www.cms.gov/medicare/icd-10/2022-icd-10-cm

Mira AI Scribe

The Mira AI Scribe captures the spinal regions affected (by name), confirms absence of definitive x-ray sacroiliac damage, and records MRI or lab findings (bone marrow edema on MRI, elevated CRP/ESR, HLA-B27 result) that substantiate the nr-axSpA diagnosis. This prevents downcoding to unspecified M45.A0 and blocks an Excludes1 conflict flag if AS codes are inadvertently suggested.

See how Mira captures M45.AB documentation