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M05.042 ICD-10-CM Code: Felty's syndrome, left hand

M05.042 maps to CMS-HCC V28 93 (RAF 0.617). Documentation must support MEAT. MEAT criteria · RAF calculator · free HCC coding tools

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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Inflammatory polyarthropathies (M05-M14)

M05.042

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

Felty's syndrome, left hand

Felty's syndrome affecting the left hand, a condition combining rheumatoid arthritis with an enlarged spleen and low white blood cell count.

Buddy the Bee presenting code insight

Buddy Insight

Felty's syndrome involving the left hand creates a devastating combination of functional disability and immune compromise that requires urgent and comprehensive care.

CMS-HCC V28

HCC 93

RAF 0.617

CMS-HCC V24

HCC 40

RAF 0.421

ACA/HHS

HCC 56

Varies by metal level

ESRD/PACE

HCC 40

RAF 0.058

RXHCC

HCC 83

RAF 0.222

Code Book Path

Official
M05.0Felty's syndrome
M05.04Felty's syndrome, hand
M05.042Felty's syndrome, left hand

Inclusion Terms

Official
  • Felty's syndrome, metacarpus and phalanges

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M05.042 in this effective period.

Related Child Codes

Official
M05.041Felty's syndrome, right hand
M05.049Felty's syndrome, unspecified hand

Includes

Official

ICD-10-CM does not list Includes notes for M05.042 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M05.042 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M05.042 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M05.042 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M05.042 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Clear documentation of rheumatoid arthritis specifically affecting the left hand
Clinical or imaging evidence of splenomegaly
Laboratory confirmation of neutropenia with quantitative white cell counts
Left hand laterality explicitly documented

MEAT Support

HCC Buddy guidance
Clear documentation of rheumatoid arthritis specifically affecting the left hand
Clinical or imaging evidence of splenomegaly
Laboratory confirmation of neutropenia with quantitative white cell counts
Left hand laterality explicitly documented

Audit Caution

HCC Buddy guidance
Using right hand code when left hand is specifically documented
Failing to recognize Felty's syndrome when all components are present
Missing the systemic implications of the complete syndrome
Not verifying laboratory confirmation of neutropenia

Common Mistakes

HCC Buddy guidance
M05.041 — Same condition but affecting right hand instead of left
M05.9 — Seropositive rheumatoid arthritis without the complete Felty's triad
M06.9 — Rheumatoid arthritis unspecified without hematologic involvement
D70.4 — Cyclic neutropenia without rheumatoid arthritis context

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 M05.042 an HCC code?

Yes. M05.042 (Felty's syndrome, left hand) maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under V24), with a community non-dual aged RAF of 0.617. It is billable for payment year 2026.

Coder answer: M05.042 is billable and maps to V28 HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
M05.042
Description
Felty's syndrome, left hand
HCC (V28)
HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
RAF
0.617
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
0.617
V24HCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease
0.421
ESRDHCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease
0.058
RxHCCHCC 83, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease
0.222

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 M05.042 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for M05.042

For M05.042 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 M05.042 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M05.042 is the ICD-10-CM diagnosis code for felty's syndrome, left hand. Felty's syndrome affecting the left hand, a condition combining rheumatoid arthritis with an enlarged spleen and low white blood cell count. M05.042 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering inflammatory polyarthropathies (m05-m14).

Under the CMS-HCC V28 risk adjustment model, M05.042 maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders (HCC 93) with a community, non-dual, aged base RAF weight of 0.617. Under the older CMS-HCC V24 model, M05.042 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 40) with a community, non-dual, aged base RAF weight of 0.421. 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 specifies left hand involvement; do not use if right hand or bilateral involvement is documented. Because M05.042 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 M05.042 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •This code specifies left hand involvement; do not use if right hand or bilateral involvement is documented
  • •Confirm documentation supports Felty's syndrome diagnosis including systemic manifestations beyond joint involvement

Clinical Significance

Felty's syndrome involving the left hand creates a devastating combination of functional disability and immune compromise that requires urgent and comprehensive care. Hand involvement severely impacts daily activities while the associated neutropenia and splenomegaly create life-threatening infection risks demanding specialized management protocols.

Documentation Requirements

  • ✓Clear documentation of rheumatoid arthritis specifically affecting the left hand
  • ✓Clinical or imaging evidence of splenomegaly
  • ✓Laboratory confirmation of neutropenia with quantitative white cell counts
  • ✓Left hand laterality explicitly documented
  • ✓Assessment of hand function and dexterity limitations
  • ✓Infection screening and immune status evaluation
  • ✓Treatment regimen including immunomodulatory agents
  • ✓Occupational therapy and adaptive equipment needs documentation

Commonly Confused Codes

  • •M05.041: Same condition but affecting right hand instead of left
  • •M05.9: Seropositive rheumatoid arthritis without the complete Felty's triad
  • •M06.9: Rheumatoid arthritis unspecified without hematologic involvement
  • •D70.4: Cyclic neutropenia without rheumatoid arthritis context
  • •M79.3: Panniculitis when interpreting hand inflammation incorrectly

Child Codes

M05.041Felty's syndrome, right hand
HCC 93
M05.042Felty's syndrome, left hand
HCC 93
M05.049Felty's syndrome, unspecified hand
HCC 93

Code Hierarchy

└M05Rheumatoid arthritis with rheumatoid factor└M05.0Felty's syndrome└M05.04Felty's syndrome, hand└M05.042Felty's syndrome, left hand
└M05.042Felty's syndrome, left hand

Because M05.042 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.

M05.042 maps to CMS-HCC V28 category 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. Because M05.042 carries a payment HCC, you can see what it adds to a RAF score and check the documentation the chart needs before it is submitted.

More on M05.042

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