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M45 ICD-10-CM Code: Ankylosing spondylitis

Billing Status: NO. This is a clinician non-billable / parent hierarchy grouping in the ICD-10-CM system.

Coding at a Glance

Tabular directives
1 inclusion term · 2 Excludes1 · 1 Excludes2

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for M45 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Inclusion Terms

Alternative terms the tabular list files under this code.

  • Rheumatoid arthritis of spine

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

Coder workflow for M45

MedCoder structured workflow — derived from this code’s own official record

Before you code M45

  1. M45 is not reportable as written. Select the more specific code beneath it that the documentation supports. Codes are reported to the highest level of specificity the classification provides (Guidelines I.B.2).

    ReviewM45.0, M45.1, M45.2, M45.3, M45.4, M45.5, M45.6, M45.7, M45.8, M45.9, M45.A

    See the relationships section · Guide: How to choose an ICD-10-CM code →

  2. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with M45. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

    See the official tabular notes

Choose the right path

  1. Does the documentation support one of the more specific codes beneath M45?
    Yes → Select that code and continue the checks below on its own page.
    No → M45 cannot be reported as written; query for the specificity its subcategory needs.

    ReviewM45.0, M45.1, M45.2, M45.3, M45.4, M45.5, M45.6, M45.7, M45.8, M45.9, M45.A

  2. Does the documentation support a condition named in M45’s Excludes1 note?
    Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
    No → Continue.

    ReviewM02.3, M08.1

Consider M45. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).

Official instructions as workflow

  • Excludes1 — check before selecting M45(2 notes)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with M45: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    CompareM02.3, M08.1

    See the official tabular notes · Guidelines I.A.12.a

  • Excludes2 — not part of M45(1 note)

    Coding workflow: The conditions named in this note are not included in M45. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

    CompareM35.2

    See the official tabular notes · Guidelines I.A.12.b

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: Both the condition M45 describes and a condition named in its Excludes1 note are documented for the same encounter.

Coding question: Can both codes be reported?

Path: Review the Excludes1 note and the excluded code, and look for a provider statement on whether the two conditions are related.

Reason: Excludes1 means the two are not coded together; the exception is when the record shows the conditions are unrelated to each other (Guidelines I.A.12.a).

ReviewM02.3, M08.1

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Ankylosing spondylitis is a non-billable ICD-10-CM category code (M45). A more specific billable subcode must be selected for claims submission.

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Verify Before Coding

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name M45 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 2 Excludes1 notes across 2 chapters: G55 — Nerve root and plexus compressions in diseases classified elsewhere, M05 — Rheumatoid arthritis with rheumatoid factor.

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 7 Excludes2 notes: M20 — Acquired deformities of fingers and toes, M20-M25 — Other joint disorders (M20-M25), M21 — Other acquired deformities of limbs, M22 — Disorder of patella, M23 — Internal derangement of knee, M24 — Other specific joint derangements, M25 — Other joint disorder, not elsewhere classified.

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

Referenced by 1 Code First instruction: J99 — Respiratory disorders in diseases classified elsewhere.

Each of these codes carries a Code First note naming this condition — when that code is reported, THIS code is sequenced first, ahead of it.

Contextual Map

Every relationship of M45 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run M45 with these 13 related codes in Claim Check

Hierarchy

Excludes1

Excludes2

Referenced by Excludes1 notes

Referenced by Excludes2 notes

Referenced by Code First instructions

Nearest codes (21)

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Common coding questions

Can M45 be billed directly?

No. M45 (Ankylosing spondylitis) is a non-billable ICD-10-CM category code. A more specific billable subcode must be selected based on clinical documentation.

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "M45 — Ankylosing spondylitis." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/m45-ankylosing-spondylitis

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Ankylosing spondylitis

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027 (effective October 1, 2026), and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to M45 in its code family, with their registry titles.