Diagnostic Performance and Predictive Value of Rheu- matoid Factor, Anti-citrullinated Peptide Antibodies, and the HLA Shared Epitope for Diagnosis of Rheuma-

Rheumatoid factor (RF) is currently the most accepted laboratory test for rheumatoid arthritis (RA) and is part of the revised American College of Rheumatology (ACR) classification criteria for RA (1). The specificity of RF is, however, often low (2–5). A newer diagnostic marker for RA is anti-citrullinated peptide antibodies (ACPAs), which can be identified by tests such as a line immuno-assay (LIATM) for the detection of anti-pepA and anti-pepB antibodies (6), the anti-cyclic citrullinated peptide ELISA (7), an ELISA using citrullinated recombinant rat filaggrin (8), and an ELISA using deiminated fibrinogen (9). ACPAs have excellent specificity (89–100%) for RA, with good sensitivity (41–80%) (3–7, 10–14, 16). Further-more, the HLA shared epitope (SE) has been described, which is found more often in RA patients than in control