M01.X21
BillableDirect infection of right elbow in infectious and parasitic diseases classified elsewhere
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M01.X21 an HCC code?
Yes. M01.X21 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 M01.X21
For M01.X21to 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 M01.X21 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M01.X21 is the ICD-10-CM diagnosis code for direct infection of right elbow in infectious and parasitic diseases classified elsewhere. Direct infection of the right elbow joint resulting from an infectious or parasitic disease classified elsewhere. M01.X21 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, M01.X21 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, M01.X21 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.
Must be accompanied by a code identifying the underlying infectious disease (Chapter 1). Because M01.X21 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 M01.X21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Must be accompanied by a code identifying the underlying infectious disease (Chapter 1)
- •Confirm right elbow is documented; do not assume laterality
Clinical Significance
Direct infectious involvement of the right elbow joint secondary to classified infectious or parasitic diseases represents a significant complication affecting upper extremity function. This condition requires coordinated treatment of both the underlying systemic infection and local joint manifestations to prevent permanent disability.
Documentation Requirements
- ✓Clear documentation of right elbow joint infection
- ✓Primary code for underlying infectious or parasitic disease (A00-B99 range)
- ✓Evidence that joint infection is direct extension, not secondary bacterial infection
- ✓Physical examination findings of elbow joint involvement
- ✓Inflammatory markers and infection parameters in laboratory studies
- ✓Imaging confirmation of joint pathology (plain films, MRI, ultrasound)
- ✓Joint aspiration results if performed, including culture and sensitivity
- ✓Treatment plan addressing systemic infection and joint-specific therapy
Commonly Confused Codes
- •M00.921 — Pyogenic arthritis, right elbow (bacterial joint infection not from classified disease)
- •M25.521 — Pain in right elbow (joint pain without infectious etiology)
- •A18.02 — Tuberculous arthritis (when tuberculosis is the specific cause)
- •M01.X22 — Direct infection of left elbow in infectious diseases classified elsewhere