ICD-10 Code M05.A – Abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code M05.A – Abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis
What it is
This code identifies rheumatoid arthritis documented with abnormal rheumatoid factor and anti-citrullinated protein antibody findings. Use it when the record supports seropositive rheumatoid arthritis with these abnormal antibody results.
Clinical signs
Typical findings include chronic inflammatory joint pain, swelling, stiffness, and symmetric small-joint involvement. Clinical features vary; refer to documentation for the specific pattern and confirmed serologic results.
When to use this code
Use this code when the provider explicitly links rheumatoid arthritis with abnormal rheumatoid factor and anti-citrullinated protein antibody results. It is appropriate when the diagnosis is established and the antibody abnormality is part of the documented condition. Do not infer the link from labs alone.
Do not use for
Do not use it for isolated abnormal antibody tests without rheumatoid arthritis. Do not use it when the chart does not clearly document the association; check documentation.
Coding tip
Verify that both the rheumatoid arthritis diagnosis and the abnormal antibody findings are documented together before assigning M05.A.