title: Third generation anti-citrullinated peptide antibody assay is a sensitive marker in rheumatoid factor negative rheumatoid arthritis.
abstract: BACKGROUND
  We compared 2 anti-citrullinated protein antibody (ACPA) assays using a routine patient cohort.
  
  
  METHODS
  Two-hundred ninety-five sera were collected from patients for whom ACPA was ordered and tested for ACPA by QUANTA Lite® CCP 3 (INOVA Diagnostics, Inc., San Diego) and EliA® CCP (CCP, Phadia, Germany). Rheumatoid factor (RF) was determined using Quantex RF(II) (Biokit, Spain).
  
  
  RESULTS
  Acceptable qualitative (96.6%, kappa=0.93) and quantitative agreements (Spearman rho=0.77; p<0.0001) were observed between the two ACPA assays. Nine samples were CCP3+/CCP2- and one sample was CCP2+/CCP3-. Of the 9 CCP3+/CCP2- patients, 6 (66.7%) had RA, one patient had ankylosing spondylitis, one osteoarthritis and one psoriatic arthritis. The CCP3-/CCP2+ patient had juvenile RA. At the manufacturer's cut-offs, the sensitivities and specificities were 77.3%/98.1% (CCP2), 81.6%/96.8% (CCP3) and 65.2%/89.6% (RF), respectively. At 98.7% specificity level, the sensitivities in the total cohort were 59.6% (CCP2) and 69.5% (CCP3) while the sensitivities in the RF-negative group were 49.0% (CCP2) and 57.1% (CCP3). In the RF-negative group, sensitivities for patients with a disease duration of ≤ 5years were 38.7% (CCP2) and 51.6% (CCP3).
  
  
  CONCLUSIONS
  Discrimination between RA and non-RA patients was better using CCP3, most pronounced in RF-negative RA.
authors.affiliation: Center for Rheumatic Diseases, Neuss, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Swart
authors.forename: Rufus W
authors.initials: RW
authors.lastname: Burlingame
authors.forename: Irmgard
authors.initials: I
authors.lastname: Gürtler
authors.forename: Michael
authors.initials: M
authors.lastname: Mahler
mesh_terms: D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000276:immunology; D001323:Autoantibodies / Q000097:blood* / Q000276:immunology; D015415:Biomarkers / Q000097:blood; D005260:Female; D006801:Humans; D007118:Immunoassay; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000097:blood* / Q000276:immunology; D012680:Sensitivity and Specificity
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide