title: Diagnostic accuracy of the anti-citrulline antibody assay for rheumatoid arthritis.
abstract: BACKGROUND
  Rheumatoid arthritis (RA) is the most common autoimmune rheumatic disease, but specific and practicable tests for its diagnosis are lacking. We evaluated the diagnostic accuracy of a new commercial ELISA in detecting anti-cyclic citrullinated peptide (CCP) antibodies for the diagnosis of RA.
  
  
  METHODS
  Anti-CCP antibodies were determined in 330 serum samples: 98 from RA patients and 232 from controls, including patients with connective tissue diseases, other rheumatic diseases, viral infections, Lyme disease, autoimmune thyroiditis, cancer, and monoclonal gammopathy, and sex- and age-matched healthy subjects. Intra- and interassay CVs were 5-13% and 9-17%, respectively. Rheumatoid factor (RF) was also assayed in every sample, and results were compared to anti-CCP for sensitivity and specificity.
  
  
  RESULTS
  At a cutoff value of 50 units, sensitivity was 41% (confidence interval, 31-50%) and specificity was 97.8% (95-100%). Anti-CCP-positive RA patients had a mean antibody concentration of 1100 units (range, 57-3419 units), and anti-CCP-negative RA patients and controls had mean values of 7.6 and 6.8 units, respectively (range, 1-39 units). The area under the ROC curve was 0.71 (95% confidence interval, 0.63-0.78). RF had a higher sensitivity (62%) and a lower specificity (84%) than anti-CCP. When the two antibodies were used together, specificity was 99.6%.
  
  
  CONCLUSIONS
  Anti-CCP antibody testing may be useful if performed concomitantly with RF assay to diagnose patients with suspected early RA.
authors.affiliation: Laboratorio di Patologia Clinica, Ospedale Civile, 30027 S. Donà di Piave (VE), Italy. nbizzaro@dacos.it
authors.forename: N
authors.initials: N
authors.lastname: Bizzaro
authors.forename: G
authors.initials: G
authors.lastname: Mazzanti
authors.forename: E
authors.initials: E
authors.lastname: Tonutti
authors.forename: D
authors.initials: D
authors.lastname: Villalta
authors.forename: R
authors.initials: R
authors.lastname: Tozzoli
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000906:Antibodies / Q000032:analysis*; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000276:immunology; D015415:Biomarkers / Q000032:analysis; D002956:Citrulline / Q000276:immunology*; D019937:Diagnostic Techniques and Procedures; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000276:immunology; D012217:Rheumatoid Factor / Q000032:analysis; D012680:Sensitivity and Specificity
chemical_list: D000906:Antibodies; D015415:Biomarkers; D010456:Peptides, Cyclic; D002956:Citrulline; D012217:Rheumatoid Factor