M86.421
BillableChronic osteomyelitis with draining sinus, right humerus
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.421 an HCC code?
Yes. M86.421 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 M86.421
For M86.421 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 M86.421 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.421 is the ICD-10-CM diagnosis code for chronic osteomyelitis with draining sinus, right humerus. A long-term bone infection in the right upper arm bone (humerus) with an open drainage tract that allows infected material to drain through the skin. M86.421 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, M86.421 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, M86.421 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.
Confirm laterality is documented as right; if left is documented, use M86.422 instead. Because M86.421 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 M86.421 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Confirm laterality is documented as right; if left is documented, use M86.422 instead
- •Ensure documentation supports both chronic osteomyelitis diagnosis and the presence of a draining sinus
Clinical Significance
Chronic osteomyelitis with draining sinus of the right humerus represents a severe bone infection of the upper arm with persistent drainage, significantly impacting arm function and quality of life. The draining sinus indicates treatment-resistant disease requiring comprehensive management and monitoring for complications.
Documentation Requirements
- ✓Specific documentation of right humerus involvement
- ✓Evidence of chronicity (>6 weeks duration or recurrent episodes)
- ✓Confirmation of active draining sinus tract from humerus
- ✓Imaging findings demonstrating chronic osteomyelitic changes
- ✓Clinical assessment of right arm function and drainage
- ✓Laboratory markers supporting chronic infectious process
- ✓Treatment history addressing infection and sinus management
- ✓Provider assessment confirming chronic osteomyelitis with drainage
Commonly Confused Codes
- •M86.521 — Other chronic hematogenous osteomyelitis, right humerus, no drainage
- •M86.422 — Same condition affecting left humerus
- •M86.321 — Chronic multifocal osteomyelitis, right humerus, no drainage
- •M86.121 — Acute osteomyelitis of right humerus, acute vs chronic
- •L02.421 — Cutaneous abscess of right upper limb, superficial vs bone