M00.9
BillablePyogenic arthritis, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M00.9 an HCC code?
Yes. M00.9 maps to Bone/Joint/Muscle Infections/Necrosis under the CMS-HCC V28 risk adjustment model (and Bone/Joint/Muscle Infections/Necrosis under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. 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.
MEAT Criteria for M00.9
For M00.9to 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.
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 Infections/Necrosis (HCC 92) with a community, non-dual, aged base RAF weight of 0.209. Under the older V24 model, M00.9 mapped to the same category but with a base RAF weight of 0.482 — V28 recalibrated weights across the entire model. 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)