M86.8X9 ICD-10-CM Code: Other osteomyelitis, unspecified sites
HCC Buddy Code Card
Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.
FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Other osteopathies (M86-M90)
M86.8X9
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceOther osteomyelitis, unspecified sites
A bone infection (osteomyelitis) affecting an unspecified location that doesn't fit into other specific osteomyelitis categories.
Buddy Insight
Other osteomyelitis at unspecified sites represents bone infection that doesn't fit standard acute or chronic patterns and lacks specific anatomical documentation.
CMS-HCC V28
MappedHCC 92
RAF 0.479
CMS-HCC V24
MappedHCC 39
RAF 0.401
ACA/HHS
MappedHCC 55
Varies by metal level
ESRD/PACE
MappedHCC 39
RAF 0.092
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for M86.8X9 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M86.8X9 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M86.8X9 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for M86.8X9 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M86.8X9 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M86.8X9 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M86.8X9 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is M86.8X9 an HCC code?
Yes. M86.8X9 (Other osteomyelitis, unspecified sites) maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis under the CMS-HCC V28 risk adjustment model (and Bone/Joint/Muscle Infections/Necrosis under V24), with a community non-dual aged RAF of 0.479. It is billable for payment year 2026.
Coder answer: M86.8X9 is billable and maps to V28 HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- M86.8X9
- Description
- Other osteomyelitis, unspecified sites
- HCC (V28)
- HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
- RAF
- 0.479
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. 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.
Work M86.8X9 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for M86.8X9
For M86.8X9 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 M86.8X9 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
M86.8X9 is the ICD-10-CM diagnosis code for other osteomyelitis, unspecified sites. A bone infection (osteomyelitis) affecting an unspecified location that doesn't fit into other specific osteomyelitis categories. M86.8X9 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, M86.8X9 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis (HCC 92) with a community, non-dual, aged base RAF weight of 0.479. Under the older CMS-HCC V24 model, M86.8X9 maps to Bone/Joint/Muscle Infections/Necrosis (HCC 39) with a community, non-dual, aged base RAF weight of 0.401. 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 is the least specific code in the 'other osteomyelitis' category; use only when the site cannot be determined. Because M86.8X9 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 M86.8X9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is the least specific code in the 'other osteomyelitis' category; use only when the site cannot be determined
- •Query the provider if possible to obtain a more specific anatomical location for better coding accuracy
Clinical Significance
Other osteomyelitis at unspecified sites represents bone infection that doesn't fit standard acute or chronic patterns and lacks specific anatomical documentation. This indicates complex clinical scenarios where infection characteristics don't conform to typical classifications, requiring careful evaluation to determine appropriate treatment approaches despite incomplete localization information.
Documentation Requirements
- ✓Documentation of osteomyelitis diagnosis with atypical features
- ✓Clinical justification for 'other' versus acute or chronic classification
- ✓Available information about potential anatomical involvement
- ✓Supporting diagnostic studies confirming bone infection
- ✓Laboratory markers supporting infection diagnosis
- ✓Treatment plan addressing diagnostic uncertainty
- ✓Explanation for why specific anatomical site cannot be determined
- ✓Documentation of unique clinical characteristics