ICD-10 Code M05.779 – Rheumatoid arthritis with rheumatoid factor of unspecified ankle and foot without organ or systems involvement (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code M05.779 – Rheumatoid arthritis with rheumatoid factor of unspecified ankle and foot without organ or systems involvement
What it is
This code identifies rheumatoid arthritis with positive rheumatoid factor affecting an unspecified ankle and foot, without documented organ or system involvement. Use it when the record supports RA in these joints but does not specify laterality.
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 evidence of rheumatoid factor positivity and joint involvement.
When to use this code
Use M05.779 when the provider documents rheumatoid arthritis, rheumatoid factor positivity, and involvement of an unspecified ankle and foot. It is appropriate when the note does not identify right or left side and does not describe extra-articular disease.
Code this diagnosis from clear assessment or problem-list documentation, not from suspicion alone. If the chart says “unspecified ankle and foot” or gives no laterality, this code fits better than a more specific joint code.
Do not use for
Do not use this code if rheumatoid factor is not documented or if the arthritis is another type, such as seronegative or degenerative arthritis. Check documentation when laterality or systemic involvement is recorded.
Coding tip
Verify both the rheumatoid factor status and the exact joint wording before assigning this code.