Anti-cyclic citrullinated peptide autoantibodies measured by an automated enzyme immunoassay: analytical performance and clinical correlations.

ABSTRACT

BACKGROUND: Autoantibodies against cyclic citrullinated peptide (anti-CCP) are considered to be a sensitive and specific marker for rheumatoid arthritis (RA). This study evaluated the analytical performance and clinical correlation of an automated enzyme immunoassay (DSX, DINEX Technologies), for the detection of anti-CCP autoantibodies (DIASTAT anti-CCP, Axis-Shield, DUNDEE UK). METHODS: Commercial controls and serum pools were used to determine its precision, analytical sensitivity, functional sensitivity and linearity. Sera from 83 patients with established RA and from 140 controls, including patients with various autoimmune diseases, viral infections and cancer, as well as sex- and age-matched healthy subjects, were studied. The rheumatoid factor (RF) was also assayed in each sample, and the results were compared to the anti-CCP findings. RESULTS: The total imprecision (CV%) was 4.7-7.2% for concentrations ranging between 1.98 and 71.81 U/mL. The lower detection limit was 0.038 U/mL. At a cut-off of 5 U/mL, the sensitivity and specificity for RA were 67.5% and 99.3%, respectively. The RF had a sensitivity of 66.3% and a lower specificity 82.1% than anti-CCP. When the two antibodies were used together, the specificity was 99.1%. CONCLUSIONS: The anti-CCP assay we examined on a fully automated system showed a good analytical performance (analytical and functional sensitivity, linearity) and good clinical correlation. We conclude that this system can provide rapid, useful data.