ICD-10 Code M05.879 – Other rheumatoid arthritis with rheumatoid factor of unspecified ankle and foot (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code M05.879 – Other rheumatoid arthritis with rheumatoid factor of unspecified ankle and foot
What it is
This code identifies rheumatoid arthritis with rheumatoid factor that affects the ankle and foot, but the specific joint is not further described. Use it when documentation shows RA with RF positivity in these locations.
Clinical signs
Typical findings include inflammatory joint pain, swelling, stiffness, and reduced range of motion in the ankle or foot. Clinical features vary; refer to documentation for the exact joint involvement and laterality.
When to use this code
Use this code when the record states rheumatoid arthritis with rheumatoid factor and the ankle or foot is involved, but the note does not specify a more exact site. It is appropriate for nonspecific ankle-foot involvement documented by the clinician. If the chart identifies a different rheumatoid arthritis subtype, choose that code instead.
Do not use for
Do not use it for rheumatoid arthritis without rheumatoid factor, or when the affected site is clearly documented elsewhere. Check documentation if the note only says arthritis, joint pain, or foot pain without confirming rheumatoid arthritis.
Coding tip
Confirm both rheumatoid factor positivity and ankle/foot involvement in the provider note before assigning M05.879.