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Diagnostic impact of contemporary biomarker assays for rheumatoid arthritis

Objective: The impetus towards early treatment for patients with rheumatoid arthritis (RA) requires more reliable disease markers than the non‐specific immunoglobulin M (IgM) rheumatoid factor (RF). To determine the accuracy of newer biomarkers for RA testing for antibody against cyclic citrullinated peptides (anti‐CCP Ab), IgA‐ and IgG‐RF and cartilage oligomeric matrix protein (COMP) levels, measured by enzyme‐linked immunosorbent assay (ELISA), were compared with IgM‐RF isotyping. Methods: Serum samples were investigated in patients with an established diagnosis of RA (n = 54), ankylosing spondylitis (AS) (n = 36), and non‐inflammatory conditions (n = 18) (cohort A), and in 234 consecutive outpatients in a blinded fashion (cohort B). Non‐parametric analysis of areas under the curve (AUC) of receiver operator characteristics were performed. Results: The presence of anti‐CCP Ab had the highest accuracy (96%) in distinguishing RA patients in cohort A and cohort B (accuracy 83%), and in both cohorts combined (accuracy 87%). This was related to the high specificity of anti‐CCP Ab for RA (95–96%), even though IgM‐RF was the most sensitive test (87–96%). Sensitivity (15–48%) and specificity (66–69%) of COMP as a marker for RA was low. Combining results of anti‐CCP Ab and IgM‐RF or any of the other assays did not increase the diagnostic accuracy for RA. Conclusion: The presence of anti‐CCP Ab is the most accurate biomarker for RA in both selected and unselected cohorts, while the COMP assay is not very useful in RA diagnosis. Combining assays for anti‐CCP Ab and IgM‐RF or IgA‐RF does not enhance RA diagnosis.