M86.221
BillableSubacute osteomyelitis, right humerus
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.221 an HCC code?
Yes. M86.221 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 M86.221
For M86.221 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 M86.221 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.221 is the ICD-10-CM diagnosis code for subacute osteomyelitis, right humerus. A bone infection in the right upper arm bone (humerus) that develops gradually over weeks to months, causing inflammation and potential bone damage. M86.221 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering other osteopathies (m86-m90).
Under the CMS-HCC V28 risk adjustment model, M86.221 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, M86.221 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.
Verify the infection site is specifically the humerus and not the shoulder joint itself. Because M86.221 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 M86.221 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify the infection site is specifically the humerus and not the shoulder joint itself
- •Document the specific location on the humerus (proximal, shaft, or distal) if available for additional specificity
Clinical Significance
Subacute osteomyelitis of the right humerus represents a bone infection with gradual onset affecting the major upper arm bone over weeks to months. This intermediate phase infection requires monitoring to prevent progression to chronic osteomyelitis and preserve upper extremity function.
Documentation Requirements
- ✓Specific identification of right humerus involvement
- ✓Documentation of subacute infection timeline
- ✓Clinical evidence of humeral bone infection
- ✓Imaging confirmation of osteomyelitis in right humerus
- ✓Laboratory evidence of ongoing bone infection
- ✓Assessment of arm function and range of motion
- ✓Documentation of symptom progression
- ✓Treatment plan to prevent chronic conversion
Commonly Confused Codes
- •M86121 — Other acute osteomyelitis of right humerus
- •M86621 — Chronic osteomyelitis with draining sinus of right humerus
- •M86321 — Chronic multifocal osteomyelitis of right humerus
- •M25511 — Pain in right shoulder
- •S42.301A — Unspecified fracture of shaft of right humerus