M05.021 ICD-10-CM Code: Felty's syndrome, right elbow
HCC Buddy Code Card
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Inflammatory polyarthropathies (M05-M14)
M05.021
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceFelty's syndrome, right elbow
Felty's syndrome affecting the right elbow, characterized by rheumatoid arthritis, enlarged spleen, and low white blood cell count.
Buddy Insight
Felty's syndrome affecting the right elbow represents a severe systemic rheumatoid condition that combines joint inflammation with dangerous hematologic abnormalities.
CMS-HCC V28
MappedHCC 93
RAF 0.175
CMS-HCC V24
MappedHCC 40
RAF 0.307
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 40
RAF 0.0
RXHCC
MappedHCC 83
RAF 0.0
Code Trumping
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Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for M05.021 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M05.021 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M05.021 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for M05.021 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M05.021 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M05.021 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M05.021 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is M05.021 an HCC code?
Yes. M05.021 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease 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 M05.021
For M05.021to 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 M05.021 during that encounter, not just copy-forwarded from a problem list.
What This Code Means
M05.021 is the ICD-10-CM diagnosis code for felty's syndrome, right elbow. Felty's syndrome affecting the right elbow, characterized by rheumatoid arthritis, enlarged spleen, and low white blood cell count. M05.021 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, M05.021 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 93) with a community, non-dual, aged base RAF weight of 0.175. Under the older V24 model, M05.021 mapped to the same category but with a base RAF weight of 0.307, 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.
Ensure documentation specifically mentions right elbow involvement. Because M05.021 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 M05.021 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Ensure documentation specifically mentions right elbow involvement
- •This code should not be used for bilateral or left elbow involvement
Clinical Significance
Felty's syndrome affecting the right elbow represents a severe systemic rheumatoid condition that combines joint inflammation with dangerous hematologic abnormalities. This diagnosis requires urgent attention due to the immunocompromised state from neutropenia and the potential for serious infectious complications.
Documentation Requirements
- ✓Clear documentation of rheumatoid arthritis specifically affecting the right elbow
- ✓Evidence of splenomegaly through physical examination or imaging
- ✓Laboratory confirmation of neutropenia with specific cell counts
- ✓Right elbow joint involvement explicitly documented
- ✓Assessment of joint function and inflammatory markers
- ✓History of recurrent infections or immune dysfunction
- ✓Current immunosuppressive therapy and monitoring protocols
- ✓Exclusion of other causes of neutropenia and splenomegaly
Commonly Confused Codes
- •M05.9: Seropositive rheumatoid arthritis without the Felty's syndrome components
- •M06.022: Rheumatoid bursitis of left elbow, wrong laterality and condition type
- •D70.9: Neutropenia without the rheumatoid arthritis component
- •M05.029: Same condition but unspecified elbow when right is documented
- •K63.2: When spleen findings are misinterpreted as other abdominal conditions