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

M00.9 maps to CMS-HCC V28 92 (RAF 0.479). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC Buddy coding tools

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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Infectious arthropathies (M00-M02)

M00.9

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Pyogenic arthritis, unspecified

Infection of one or more joints caused by bacteria, but the specific type of bacteria is not identified.

Buddy the Bee presenting code insight

Buddy Insight

Pyogenic arthritis unspecified represents bacterial joint infection where the causative organism has not been identified, requiring broad-spectrum antibiotic coverage until culture results are available.

CMS-HCC V28

HCC 92

RAF 0.479

CMS-HCC V24

HCC 39

RAF 0.401

ACA/HHS

HCC 55

Varies by metal level

ESRD/PACE

HCC 39

RAF 0.092

RXHCC

N/A

—

Not mapped

Code Book Path

Official
M00Pyogenic arthritis
M00.9Pyogenic arthritis, unspecified

Inclusion Terms

Official
  • Infective arthritis NOS

Excludes 2

Official
  • infection and inflammatory reaction due to internal joint prosthesis (T84.5-)

Related Child Codes

Official
M00.0Staphylococcal arthritis and polyarthritis
M00.1Pneumococcal arthritis and polyarthritis
M00.2Other streptococcal arthritis and polyarthritis
M00.8Arthritis and polyarthritis due to other bacteria

Includes

Official

ICD-10-CM does not list Includes notes for M00.9 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M00.9 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M00.9 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M00.9 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M00.9 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Evidence of bacterial joint infection (pyogenic)
Clinical presentation consistent with infectious arthritis
Laboratory workup for bacterial identification in progress
Documentation of empirical antibiotic therapy

MEAT Support

HCC Buddy guidance
Evidence of bacterial joint infection (pyogenic)
Clinical presentation consistent with infectious arthritis
Laboratory workup for bacterial identification in progress
Documentation of empirical antibiotic therapy

Audit Caution

HCC Buddy guidance
Using when specific organism is documented elsewhere
Not upgrading to specific code when organism identified
Confusing with non-infectious arthritis conditions
Coding as unspecified when joint location is documented

Common Mistakes

HCC Buddy guidance
M00.00-M00.89 — Specific bacterial arthritis with identified organism
M01.X0-M01.X9 — Arthritis in infectious diseases classified elsewhere
M06.9 — Rheumatoid arthritis, unspecified (autoimmune)
M13.10 — Monoarthritis, not elsewhere classified (non-infectious)

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is M00.9 an HCC code?

Yes. M00.9 (Pyogenic arthritis, unspecified) maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis under the CMS-HCC V28 risk adjustment model (and Bone/Joint/Muscle Infections/Necrosis under V24), with a community non-dual aged RAF of 0.479. It is billable for payment year 2026.

Coder answer: M00.9 is billable and maps to V28 HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
M00.9
Description
Pyogenic arthritis, unspecified
HCC (V28)
HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
RAF
0.479
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
0.479
V24HCC 39, Bone/Joint/Muscle Infections/Necrosis
0.401
ESRDHCC 39, Bone/Joint/Muscle Infections/Necrosis
0.092

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. 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.

Work M00.9 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for M00.9

For M00.9 to 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 M00.9 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M00.9 is the ICD-10-CM diagnosis code for pyogenic arthritis, unspecified. Infection of one or more joints caused by bacteria, but the specific type of bacteria is not identified. M00.9 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering infectious arthropathies (m00-m02).

Under the CMS-HCC V28 risk adjustment model, M00.9 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis (HCC 92) with a community, non-dual, aged base RAF weight of 0.479. Under the older CMS-HCC V24 model, M00.9 maps to Bone/Joint/Muscle Infections/Necrosis (HCC 39) with a community, non-dual, aged base RAF weight of 0.401. 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.

Use this code only when the causative organism is truly unknown or not documented. Because M00.9 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 M00.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Use this code only when the causative organism is truly unknown or not documented
  • •If organism is identified, use a more specific M00 code instead

Clinical Significance

Pyogenic arthritis unspecified represents bacterial joint infection where the causative organism has not been identified, requiring broad-spectrum antibiotic coverage until culture results are available. This condition demands urgent treatment to prevent joint destruction while diagnostic workup continues.

Documentation Requirements

  • ✓Evidence of bacterial joint infection (pyogenic)
  • ✓Clinical presentation consistent with infectious arthritis
  • ✓Laboratory workup for bacterial identification in progress
  • ✓Documentation of empirical antibiotic therapy
  • ✓Joint involvement documented but organism unspecified
  • ✓Inflammatory markers elevation
  • ✓Exclusion of non-infectious causes of arthritis
  • ✓Plan for organism identification and targeted therapy

Commonly Confused Codes

  • •M00.00-M00.89: Specific bacterial arthritis with identified organism
  • •M01.X0-M01.X9: Arthritis in infectious diseases classified elsewhere
  • •M06.9: Rheumatoid arthritis, unspecified (autoimmune)
  • •M13.10: Monoarthritis, not elsewhere classified (non-infectious)
  • •M25.9: Joint disorder, unspecified (mechanical)

Child Codes

M00.0Staphylococcal arthritis and polyarthritis
M00.1Pneumococcal arthritis and polyarthritis
M00.2Other streptococcal arthritis and polyarthritis
M00.8Arthritis and polyarthritis due to other bacteria
M00.9Pyogenic arthritis, unspecified
HCC 92

Code Hierarchy

└M00Pyogenic arthritis└M00.9Pyogenic arthritis, unspecified
└M00.9Pyogenic arthritis, unspecified

Because M00.9 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

M00.9 maps to CMS-HCC V28 category 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. Because M00.9 carries a payment HCC, you can see what it adds to a RAF score and check the documentation the chart needs before it is submitted.

Work M00.9 in HCC Buddy

Open M00.9 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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