Diagnostic tests for rheumatoid arthritis: comparison of anti-cyclic citrullinated peptide antibodies, anti-keratin antibodies and IgM rheumatoid factors

Objectives. To examine the value of anti-cyclic citrullinated peptide (anti-CCP) antibodies, anti-keratin antibodies (AKA) and immunoglobulin M rheumatoid factors (IgM RF) in discriminating between rheumatoid arthritis (RA) and other rheumatic diseases, and to determine whether the clinical manifestations or severity of erosions in RA are associated with anti-CCP positivity. Methods. In a cross-sectional study, we determined the concentrations or titres of these three markers in 179 RA patients and 50 controls. Erosions were quantified using the Larsen score in 129 patients. Results. Sensitivity was highest for IgM RF (75%), followed by anti-CCP antibodies (68%) and AKA (46%). Specificity was highest for anti-CCP antibodies (96%), followed by AKA (94%) and IgM RF (74%). A correlation with clinical manifestations and severity of erosions was observed mainly for IgM RF positivity. Conclusions. With their excellent specificity, anti-CCP antibodies can be useful in establishing the diagnosis of RA, but IgM RF is a better predictor of disease severity.