M05.79
BillableRheumatoid arthritis with rheumatoid factor of multiple sites without organ or systems involvement
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M05.79 an HCC code?
Yes. M05.79 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 M05.79
For M05.79 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 M05.79 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M05.79 is the ICD-10-CM diagnosis code for rheumatoid arthritis with rheumatoid factor of multiple sites without organ or systems involvement. Rheumatoid arthritis with a positive rheumatoid factor affecting multiple joints throughout the body, without involvement of other organs or body systems. M05.79 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, M05.79 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, M05.79 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 indicates polyarticular involvement; document which specific sites are affected. Because M05.79 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 M05.79 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code indicates polyarticular involvement; document which specific sites are affected
- •Use this when three or more different joint sites are involved with rheumatoid factor positive disease
Clinical Significance
Rheumatoid arthritis with positive rheumatoid factor represents a confirmed autoimmune inflammatory arthropathy with serologic evidence of disease activity. This code specifies that the disease has not progressed to involve organs beyond the joints, which is important for tracking disease severity and progression. Risk adjustment captures this as a significant chronic condition requiring ongoing immunomodulatory therapy and monitoring.
Documentation Requirements
- ✓Clinical diagnosis of rheumatoid arthritis clearly documented by the treating provider
- ✓Rheumatoid factor lab result status (positive or negative) consistent with the code selected
- ✓Affected joint(s) specified with laterality (right, left, or bilateral)
- ✓Current disease status: active, in remission, or chronic stable
- ✓Current treatment plan including medications (disease-modifying antirheumatic drugs, biologics, nonsteroidal anti-inflammatory drugs)
- ✓Documentation confirming absence of extra-articular organ involvement (lung, heart, eye, vasculitis)
- ✓Documentation of each specific joint involved; consider coding each site individually if clinically distinct
- ✓Assessment and plan addressing rheumatoid arthritis at each encounter where it impacts care or treatment
Commonly Confused Codes
- •M06.0xx (Rheumatoid arthritis without rheumatoid factor, same site) — Use M06.0xx when rheumatoid factor test is negative; M05.7xx requires a positive rheumatoid factor result
- •M05.8xx (Other rheumatoid arthritis with rheumatoid factor, same site) — Use M05.8xx when there are other specified seropositive manifestations beyond the standard joint involvement without organ involvement
- •M06.9 (Rheumatoid arthritis, unspecified) — A nonspecific code that does not indicate rheumatoid factor status; avoid when rheumatoid factor status is known
- •M05.0x-M05.6x (Rheumatoid arthritis with organ involvement such as Felty syndrome, rheumatoid lung, vasculitis) — Use these when extra-articular manifestations are documented
- •M19.x (Osteoarthritis) — Osteoarthritis is a degenerative, non-autoimmune condition; do not confuse with rheumatoid arthritis which is inflammatory and autoimmune