What is ICD-10 code M05.161?

M05.161 is the ICD-10-CM diagnosis code for Rheumatoid lung disease with rheumatoid arthritis of right knee. A condition where rheumatoid arthritis affects the right knee and also causes inflammation in the lungs. M05.161 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M05.161 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. M05.161 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. M05.161 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.

What is the V28 vs V24 difference for M05.161?

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 M05.161, V28 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease at RAF 0.175 while V24 mapped to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease at RAF 0.307. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting M05.161?

This code requires documentation of both the lung involvement and the specific knee joint affected Verify that the patient has confirmed rheumatoid arthritis diagnosis before assigning this code Because M05.161 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.

M05.161 ICD-10 Code: Rheumatoid lung disease

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupM05.161Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

M05.161

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

Rheumatoid lung disease with rheumatoid arthritis of right knee

A condition where rheumatoid arthritis affects the right knee and also causes inflammation in the lungs.

Buddy Insight

CMS-HCC V28

Mapped

HCC 93

Rheumatoid Arthritis and Infl...

RAF 0.175

CMS-HCC V24

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

RAF 0.307

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

RAF 0.0

RXHCC

Mapped

HCC 83

Rheumatoid Arthritis and Infl...

RAF 0.0

Code Trumping

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Code Book Path

Official

M05.1Rheumatoid lung disease with rheumatoid arthritis

M05.16Rheumatoid lung disease with rheumatoid arthritis of knee

M05.161Rheumatoid lung disease with rheumatoid arthritis of right knee

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for M05.161 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M05.161 in this effective period.

Related Child Codes

Official

M05.162Rheumatoid lung disease with rheumatoid arthritis of left knee

M05.169Rheumatoid lung disease with rheumatoid arthritis of unspecified knee

Includes

Official

ICD-10-CM does not list Includes notes for M05.161 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M05.161 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M05.161 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M05.161 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M05.161 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Confirmed rheumatoid arthritis with positive serological testing

Documentation of right knee joint involvement with inflammatory changes

Evidence of rheumatoid lung disease through appropriate diagnostic studies

Specific notation of right-sided knee involvement

MEAT Support

HCC Buddy guidance

Confirmed rheumatoid arthritis with positive serological testing

Documentation of right knee joint involvement with inflammatory changes

Evidence of rheumatoid lung disease through appropriate diagnostic studies

Specific notation of right-sided knee involvement

Audit Caution

HCC Buddy guidance

Confusing right and left knee documentation

Using when lung disease etiology is not confirmed as rheumatoid

Missing specific documentation of right knee involvement

Failing to verify presence of both knee RA and lung disease

Common Mistakes

HCC Buddy guidance

M05.162 — Rheumatoid lung disease with RA of left knee (different laterality)

M05.169 — Rheumatoid lung disease with RA of unspecified knee (laterality not documented)

M06.061 — Rheumatoid arthritis of right knee without lung involvement

M05.151 — Rheumatoid lung disease with RA of right hip (different joint)

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 M05.161 an HCC code?

Yes. M05.161 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

V28HCC 93, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.175

V24HCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.307

ESRDHCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.000

RxHCCHCC 83, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.000

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 M05.161

For M05.161to 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 M05.161 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

M05.161 is the ICD-10-CM diagnosis code for rheumatoid lung disease with rheumatoid arthritis of right knee. A condition where rheumatoid arthritis affects the right knee and also causes inflammation in the lungs. M05.161 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, M05.161 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, M05.161 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.

This code requires documentation of both the lung involvement and the specific knee joint affected. Because M05.161 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 M05.161 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This code requires documentation of both the lung involvement and the specific knee joint affected
•Verify that the patient has confirmed rheumatoid arthritis diagnosis before assigning this code

Clinical Significance

Indicates advanced rheumatoid arthritis with right knee involvement and concurrent pulmonary manifestations, representing severe systemic disease with significant mobility impact and respiratory complications. This condition requires intensive management due to weight-bearing joint involvement and extra-articular manifestations.

Documentation Requirements

✓Confirmed rheumatoid arthritis with positive serological testing
✓Documentation of right knee joint involvement with inflammatory changes
✓Evidence of rheumatoid lung disease through appropriate diagnostic studies
✓Specific notation of right-sided knee involvement
✓Clinical correlation between RA and pulmonary findings
✓Assessment of knee function and mobility limitations
✓Treatment plan addressing both joint preservation and pulmonary management

Commonly Confused Codes

•M05.162: Rheumatoid lung disease with RA of left knee (different laterality)
•M05.169: Rheumatoid lung disease with RA of unspecified knee (laterality not documented)
•M06.061: Rheumatoid arthritis of right knee without lung involvement
•M05.151: Rheumatoid lung disease with RA of right hip (different joint)
•M05.171: Rheumatoid lung disease with RA of right ankle and foot (different location)