Correlation between serum methotrexate-polyglutamate 3 (MTX-PG3) level and disease activity in rheumatoid arthritis patients: A prospective cohort study.

Rheumatoid arthritis (RA) is one of the most common autoimmune diseases, characterized by systemic inflammation, joint destruction and disability. Methotrexate (MTX) is used as the primary treatment for RA patients. However, the response to MTX therapy is highly varied and difficult to predict.