What is ICD-10 code M86.642?

M86.642 is the ICD-10-CM diagnosis code for Other chronic osteomyelitis, left hand. A chronic bone infection affecting the bones of the left hand with ongoing inflammation and potential loss of hand function. M86.642 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M86.642 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. M86.642 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. M86.642 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does M86.642 map to under V28?

M86.642 maps to CMS-HCC V28 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis). The category number and label come from the CMS-HCC V28 model file for payment year 2026.

What does M86.642 pay in RAF?

M86.642 carries a community, non-dual, aged (CNA) RAF weight of 0.479 under CMS-HCC V28 for payment year 2026. The weight comes from the CMS V28 relative-factor file, not a hand-typed table.

What is the V28 vs V24 difference for M86.642?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For M86.642, V28 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis at RAF 0.479 while V24 mapped to Bone/Joint/Muscle Infections/Necrosis at RAF 0.401. Both models can still appear in legacy data and in payer-specific lookback periods.

What documentation supports M86.642?

Verify 'left hand' is documented and identify specific carpal, metacarpal, or phalangeal involvement if available Document any associated complications such as contractures or limited range of motion Because M86.642 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. MEAT is generic documentation evidence, not a payer-specific rule.

2026 ICD-10-CM M86.642: Other chronic

M86.642 maps to CMS-HCC V28 92 (RAF 0.479). Documentation must support MEAT. MEAT criteria · RAF calculator · free HCC coding tools

ICD-10-CM Code View

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Code lookupM86.642Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Other osteopathies (M86-M90)

M86.642

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Other chronic osteomyelitis, left hand

A chronic bone infection affecting the bones of the left hand with ongoing inflammation and potential loss of hand function.

Buddy Insight

Chronic osteomyelitis of the left hand represents a serious bone infection affecting the complex hand anatomy, severely compromising hand function and manual dexterity.

CMS-HCC V28

Mapped

HCC 92

Bone/Joint/Muscle/Severe Soft...

RAF 0.479

CMS-HCC V24

Mapped

HCC 39

Bone/Joint/Muscle Infections/...

RAF 0.401

ACA/HHS

Mapped

HCC 55

HHS-HCC 55

Varies by metal level

ESRD/PACE

Mapped

HCC 39

Bone/Joint/Muscle Infections/...

RAF 0.092

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

M86.6Other chronic osteomyelitis

M86.64Other chronic osteomyelitis, hand

M86.642Other chronic osteomyelitis, left hand

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for M86.642 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M86.642 in this effective period.

Related Child Codes

Official

M86.641Other chronic osteomyelitis, right hand

M86.649Other chronic osteomyelitis, unspecified hand

Includes

Official

ICD-10-CM does not list Includes notes for M86.642 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M86.642 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M86.642 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M86.642 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M86.642 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Confirmation of chronic nature (minimum 6 weeks duration or recurrent)

Specific documentation of left hand bone involvement

Non-hematogenous etiology (contiguous spread or direct inoculation)

Radiographic evidence of bone infection or destruction in hand

MEAT Support

HCC Buddy guidance

Confirmation of chronic nature (minimum 6 weeks duration or recurrent)

Specific documentation of left hand bone involvement

Non-hematogenous etiology (contiguous spread or direct inoculation)

Radiographic evidence of bone infection or destruction in hand

Audit Caution

HCC Buddy guidance

Distinguishing from hematogenous origin which requires different coding

Confusion with soft tissue infections that don't affect bone

Incorrectly coding acute exacerbations as new acute osteomyelitis

Using draining sinus codes without proper documentation of sinus tract

Common Mistakes

HCC Buddy guidance

M86.542 — Other chronic hematogenous osteomyelitis, left hand (hematogenous origin)

M86.641 — Other chronic osteomyelitis, right hand (different laterality)

M86.442 — Chronic osteomyelitis with draining sinus, left hand (has sinus tract)

M86.142 — Other acute osteomyelitis, left hand (acute presentation)

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 M86.642 an HCC code?

Yes. M86.642 (Other chronic osteomyelitis, left hand) 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: M86.642 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: M86.642
Description: Other chronic osteomyelitis, left hand
HCC (V28): HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
RAF: 0.479
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis

0.479

V24HCC 39, Bone/Joint/Muscle Infections/Necrosis

0.401

ESRDHCC 39, Bone/Joint/Muscle Infections/Necrosis

0.092

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 M86.642 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for M86.642

For M86.642 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 M86.642 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M86.642 is the ICD-10-CM diagnosis code for other chronic osteomyelitis, left hand. A chronic bone infection affecting the bones of the left hand with ongoing inflammation and potential loss of hand function. M86.642 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, M86.642 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, M86.642 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.

Verify 'left hand' is documented and identify specific carpal, metacarpal, or phalangeal involvement if available. Because M86.642 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 M86.642 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Verify 'left hand' is documented and identify specific carpal, metacarpal, or phalangeal involvement if available
•Document any associated complications such as contractures or limited range of motion

Clinical Significance

Chronic osteomyelitis of the left hand represents a serious bone infection affecting the complex hand anatomy, severely compromising hand function and manual dexterity. This condition significantly impacts quality of life and may require extensive rehabilitation and adaptive strategies for daily activities.

Documentation Requirements

✓Confirmation of chronic nature (minimum 6 weeks duration or recurrent)
✓Specific documentation of left hand bone involvement
✓Non-hematogenous etiology (contiguous spread or direct inoculation)
✓Radiographic evidence of bone infection or destruction in hand
✓Laboratory studies supporting chronic infection process
✓Functional assessment of left hand including grip and pinch strength
✓Documentation of antibiotic therapy and surgical interventions
✓Assessment of occupational impact and need for adaptive equipment

Commonly Confused Codes

•M86.542: Other chronic hematogenous osteomyelitis, left hand (hematogenous origin)
•M86.641: Other chronic osteomyelitis, right hand (different laterality)
•M86.442: Chronic osteomyelitis with draining sinus, left hand (has sinus tract)
•M86.142: Other acute osteomyelitis, left hand (acute presentation)
•L03.032: Cellulitis of left finger (soft tissue infection without bone involvement)