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M00.9 ICD-10-CM Code: Pyogenic arthritis, unspecified

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Tabular directives
1 inclusion term · 1 Excludes2
Risk adjustment
CMS-HCC V28: 1 category · CMS-HCC V22 category 39

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43, Appendix B.

  • MS-DRG 485 — KNEE PROCEDURES WITH PRINCIPAL DIAGNOSIS OF INFECTION WITH MCC (MDC 08)
  • MS-DRG 486 — KNEE PROCEDURES WITH PRINCIPAL DIAGNOSIS OF INFECTION WITH CC (MDC 08)
  • MS-DRG 487 — KNEE PROCEDURES WITH PRINCIPAL DIAGNOSIS OF INFECTION WITHOUT CC/MCC (MDC 08)
  • MS-DRG 548 — SEPTIC ARTHRITIS WITH MCC (MDC 08)
  • MS-DRG 549 — SEPTIC ARTHRITIS WITH CC (MDC 08)
  • MS-DRG 550 — SEPTIC ARTHRITIS WITHOUT CC/MCC (MDC 08)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Risk Adjustment (CMS-HCC)

Payment categories this diagnosis maps to under CMS-HCC V28, payment year 2026.

  • HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis

Other models: CMS-HCC V22 HCC 39

Risk scores depend on the enrollee's full accepted diagnosis set and segment; a category mapping alone does not determine payment.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for M00.9 in the official ICD-10-CM tabular list, quoted as published.

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

Notes without a marker are published on M00.9 itself; “inherited from” names the category or block whose note applies here.

Inclusion Terms

Alternative terms the tabular list files under this code.

  • Infective arthritis NOS

Excludes2 — Not Included Here

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

Source: inherited from M00

Coder workflow for M00.9

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

Before you code M00.9

  1. Unspecified does not mean incorrect. When the record gives no greater specificity, M00.9 may be the appropriate code. Check the record for detail that supports a more specific sibling. An unspecified code is for records that do not provide the detail a more specific code needs; a query, not an assumption, is the route to specificity (Guidelines I.A.9.b, I.B.18).

    ReviewM00.8

    See the relationships section · Guide: Other vs unspecified (NEC vs NOS) →

Choose the right path

  1. Does the record document the detail a more specific sibling code needs?
    Yes → Review the specific siblings in this subcategory.
    No → Continue — M00.9 is appropriate when the documentation goes no further.

    ReviewM00.8

Consider M00.9. 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).
Any detail beyond this code’s title
What the record states that a more specific sibling code would capture — or its absence, which itself supports the unspecified code.

Official instructions as workflow

  • Excludes2 — not part of M00.9(1 note)

    Coding workflow: The conditions named in this note are not included in M00.9. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

    CompareT84.5

    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: The provider documents the condition in the terms of this code’s title and records no further detail.

Coding question: Is a more specific sibling code supportable?

Path: Review the specific siblings in this subcategory and what each requires the record to state.

Reason: A more specific code needs documentation of the distinguishing element; without it the unspecified code is appropriate, and a provider query is the route to specificity (Guidelines I.A.9.b, I.B.18).

ReviewM00.8

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

Pyogenic arthritis, unspecified is a billable ICD-10-CM diagnosis code (M00.9).

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

Indexed Clinical Terms (10)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Verify Before Coding

  • CC as a secondary diagnosis (FY2026). Can raise the stay's MS-DRG severity tier.

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

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: CC — Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 938 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 6 MS-DRGs: DRG 485 (MDC 08), DRG 486 (MDC 08), DRG 487 (MDC 08), DRG 548 (MDC 08), DRG 549 (MDC 08), DRG 550 (MDC 08).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):MUS001 — Infective arthritis (default); INF003 — Bacterial infections.

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis) for risk-adjusted payment.

M00.852 — Arthritis due to other bacteria, left hip, M00.859 — Arthritis due to other bacteria, unspecified hip, M00.861 — Arthritis due to other bacteria, right knee, M00.862 — Arthritis due to other bacteria, left knee, M00.869 — Arthritis due to other bacteria, unspecified knee, M00.871 — Arthritis due to other bacteria, right ankle and foot, M00.872 — Arthritis due to other bacteria, left ankle and foot, M00.879 — Arthritis due to other bacteria, unspecified ankle and foot, M00.88 — Arthritis due to other bacteria, vertebrae, M00.89 — Polyarthritis due to other bacteria, M01.X0 — Direct infection of unspecified joint in infectious and parasitic diseases classified elsewhere, M01.X11 — Direct infection of right shoulder in infectious and parasitic diseases classified elsewhere, M01.X12 — Direct infection of left shoulder in infectious and parasitic diseases classified elsewhere, M01.X19 — Direct infection of unspecified shoulder in infectious and parasitic diseases classified elsewhere, M01.X21 — Direct infection of right elbow in infectious and parasitic diseases classified elsewhere, M01.X22 — Direct infection of left elbow in infectious and parasitic diseases classified elsewhere, M01.X29 — Direct infection of unspecified elbow in infectious and parasitic diseases classified elsewhere, M01.X31 — Direct infection of right wrist in infectious and parasitic diseases classified elsewhere, M01.X32 — Direct infection of left wrist in infectious and parasitic diseases classified elsewhere, M01.X39 — Direct infection of unspecified wrist in infectious and parasitic diseases classified elsewhere, +588 more

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical categories (Infective arthritis, Bacterial infections).

M00.852 — Arthritis due to other bacteria, left hip, M00.859 — Arthritis due to other bacteria, unspecified hip, M00.861 — Arthritis due to other bacteria, right knee, M00.862 — Arthritis due to other bacteria, left knee, M00.869 — Arthritis due to other bacteria, unspecified knee, M00.871 — Arthritis due to other bacteria, right ankle and foot, M00.872 — Arthritis due to other bacteria, left ankle and foot, M00.879 — Arthritis due to other bacteria, unspecified ankle and foot, M00.88 — Arthritis due to other bacteria, vertebrae, M00.89 — Polyarthritis due to other bacteria, M01.X0 — Direct infection of unspecified joint in infectious and parasitic diseases classified elsewhere, M01.X11 — Direct infection of right shoulder in infectious and parasitic diseases classified elsewhere, M01.X12 — Direct infection of left shoulder in infectious and parasitic diseases classified elsewhere, M01.X19 — Direct infection of unspecified shoulder in infectious and parasitic diseases classified elsewhere, M01.X21 — Direct infection of right elbow in infectious and parasitic diseases classified elsewhere, M01.X22 — Direct infection of left elbow in infectious and parasitic diseases classified elsewhere, M01.X29 — Direct infection of unspecified elbow in infectious and parasitic diseases classified elsewhere, M01.X31 — Direct infection of right wrist in infectious and parasitic diseases classified elsewhere, M01.X32 — Direct infection of left wrist in infectious and parasitic diseases classified elsewhere, M01.X39 — Direct infection of unspecified wrist in infectious and parasitic diseases classified elsewhere, +411 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Arthritis, arthritic”, “Abscess”; these codes share that main term but sit in a different category of the Tabular List.

L04.1 — Acute lymphadenitis of trunk (inguinal, lymph gland or node), L04.2 — Acute lymphadenitis of upper limb (axilla, lymph gland or node), L05.01 — Pilonidal cyst with abscess (pilonidal), L40.50 — Arthropathic psoriasis, unspecified (psoriatic), L40.52 — Psoriatic arthritis mutilans (mutilans), L40.54 — Psoriatic juvenile arthropathy (juvenile, psoriatic), L51.9 — Erythema multiforme, unspecified (in, erythema, multiforme), L52 — Erythema nodosum (in, erythema, nodosum), L74.8 — Other eccrine sweat disorders (sweat gland), L75.8 — Other apocrine sweat disorders (sudoriparous), M04.1 — Periodic fever syndromes (in, Mediterranean fever, familial), M05.70 — Rheumatoid arthritis with rheumatoid factor of unspecified site without organ or systems involvement (rheumatoid, seropositive, without organ involvement), M05.71 — Rheumatoid arthritis with rheumatoid factor of shoulder without organ or systems involvement (rheumatoid, seropositive, without organ involvement, shoulder), M05.72 — Rheumatoid arthritis with rheumatoid factor of elbow without organ or systems involvement (rheumatoid, seropositive, without organ involvement, elbow), M05.73 — Rheumatoid arthritis with rheumatoid factor of wrist without organ or systems involvement (rheumatoid, seropositive, without organ involvement, wrist), M05.74 — Rheumatoid arthritis with rheumatoid factor of hand without organ or systems involvement (rheumatoid, seropositive, without organ involvement, hand joint), M05.75 — Rheumatoid arthritis with rheumatoid factor of hip without organ or systems involvement (rheumatoid, seropositive, without organ involvement, hip), M05.76 — Rheumatoid arthritis with rheumatoid factor of knee without organ or systems involvement (rheumatoid, seropositive, without organ involvement, knee), M05.77 — Rheumatoid arthritis with rheumatoid factor of ankle and foot without organ or systems involvement (rheumatoid, seropositive, without organ involvement, ankle), M05.79 — Rheumatoid arthritis with rheumatoid factor of multiple sites without organ or systems involvement (rheumatoid, seropositive, without organ involvement, multiple sites), +331 more

Contextual Map

Every relationship of M00.9 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.

Hierarchy

Clinical classification (CCSR)

Risk adjustment (CMS-HCC)

  • HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis [CMS-HCC]— CMS-HCC V28 · 2026

MS-DRG Grouper

MDC crossing

  • MDC 08 — Diseases and Disorders of the Musculoskeletal System and Connective Tissue[MDC crossing]: “Diseases and Disorders of the Musculoskeletal System and Connective Tissue — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 18,508 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries (10)

  • Abscess (connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic), knee, joint[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Arthritis, arthritic (acute) (chronic) (nonpyogenic) (subacute), pyogenic or pyemic (any site except spine)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Disease, diseased, hip (joint), suppurative[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Infection, infected, infective (opportunistic), acromioclavicular[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Infection, infected, infective (opportunistic), hip NEC (joint)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Infection, infected, infective (opportunistic), joint NEC[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Infection, infected, infective (opportunistic), knee NEC (joint)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Infection, infected, infective (opportunistic), knee NEC (joint), joint[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • and 2 more

Nearest codes (40)

Change history

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

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
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page
Risk adjustment Official source data
2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release 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. "M00.9 — Pyogenic arthritis, unspecified." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/m00.9-pyogenic-arthritis-unspecified

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Pyogenic arthritis, unspecified

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 M00.9 in its code family, with their registry titles.

View all codes in the M00 family