M86.321
BillableChronic multifocal osteomyelitis, right humerus
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.321 an HCC code?
Yes. M86.321 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 M86.321
For M86.321 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 M86.321 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.321 is the ICD-10-CM diagnosis code for chronic multifocal osteomyelitis, right humerus. A long-standing bone infection affecting multiple bones, specifically involving the right upper arm bone (humerus). M86.321 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, M86.321 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, M86.321 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.
This code indicates the right humerus is one of multiple affected sites; ensure all other involved bones are documented and coded. Because M86.321 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 M86.321 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code indicates the right humerus is one of multiple affected sites; ensure all other involved bones are documented and coded.
- •Verify that 'right' is clearly documented in the medical record before assigning this code.
Clinical Significance
Chronic multifocal osteomyelitis affecting the right humerus represents a severe bone infection with significant implications for upper extremity function and overall patient health. The multifocal nature suggests systemic involvement requiring intensive antibiotic therapy, potential surgical intervention, and long-term monitoring for complications including bone destruction and functional impairment.
Documentation Requirements
- ✓Clear documentation of chronic osteomyelitis diagnosis
- ✓Specific identification of multifocal involvement pattern
- ✓Anatomic specification of right humerus location
- ✓Evidence of active or persistent infection (cultures, imaging)
- ✓Documentation of infectious organism when identified
- ✓Treatment history including antibiotic regimens and duration
- ✓Surgical interventions, debridements, or hardware involvement
- ✓Functional assessment and impact on activities of daily living
Commonly Confused Codes
- •M86.322 — Chronic multifocal osteomyelitis, left humerus (incorrect laterality)
- •M86.621 — Other chronic osteomyelitis, right humerus (not multifocal)
- •M86.421 — Chronic osteomyelitis with draining sinus, right humerus (different subtype)
- •M86.521 — Other chronic hematogenous osteomyelitis, right humerus (different etiology)