To determine agreement among the 2010 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) criteria, a diagnosis of rheumatoid arthritis (RA) by a rheumatologist, and other criteria previously used to classify arthritis.
We used a nationwide longitudinal prospective cohort of patients with recent-onset arthritis. After 2 years, the patients were classified as receiving disease-modifying antirheumatic drugs (DMARDs), having synovitis, having joint erosions typical of RA, having a rheumatologist diagnosis of RA with >50.0% certainty, having a no better alternative diagnosis with >50.0% certainty, and having a diagnosis of RA using the 1987 ACR criteria and the 2010 ACR/EULAR criteria. Agreement among these criteria was assessed based on Cohen's kappa coefficient, where ≥0.80 = excellent, 0.60-0.79 = good, 0.40-0.59 = moderate, and <0.40 = poor.
Of the 692 evaluated patients, 544 (78.6%) had persistent arthritis (defined as synovitis, ongoing DMARD treatment, or both) after 2 years. Among these 544 patients, 496 (91.2%) were receiving DMARDs. Agreement among all criteria was poor (estimated κ = 0.09-0.43), except when including a rheumatologist diagnosis of RA with >50.0% certainty or a no better alternative diagnosis with >50.0% certainty (estimated κ = 0.69-0.81). The strongest associations with a rheumatologist diagnosis of RA with >50.0% certainty were the 2010 ACR/EULAR criteria and the combination of no better alternative diagnosis, persistent arthritis, 1987 ACR criteria, and positive anti-citrullinated protein antibody.
Rheumatologist diagnosis of RA with >50.0% certainty after 2 years agreed well with the 2010 ACR/EULAR criteria or a combination of items including no better alternative diagnosis, confirming high value as classification criteria after 2 years of followup.