title: Rheumatoid factor and antibodies to cyclic citrullinated Peptide differentiate rheumatoid arthritis from undifferentiated polyarthritis in patients with early arthritis.
abstract: OBJECTIVE
  To study the diagnostic value of IgM rheumatoid factor (RF), IgA-RF, antibodies to cyclic citrullinated peptide (anti-CCP), and combinations of these antibodies, measured at baseline, to discriminate rheumatoid arthritis (RA) from undifferentiated polyarthritis (uPA) in patients with recent onset arthritis.
  
  
  METHODS
  Patients with early arthritis with peripheral arthritis of 2 or more joints and symptom duration less than 3 years were clinically diagnosed as having RA or uPA by an experienced rheumatologist during the first year. Patients with bacterial, psoriatic, or crystal induced arthritis or spondyloarthropathy were excluded. Optimal cutoff values for serum IgM RF, IgA RF, and anti-CCP were deduced from receiver operating characteristics curves in order to predict the diagnosis of RA in early arthritis.
  
  
  RESULTS
  A total of 379 patients (69% female, median age 57 yrs, range 17-86 yrs) were studied; 258 patients were clinically diagnosed as RA and 121 as uPA. Both IgM-RF > 40 IU/ml and anti-CCP > 50 AU/ml showed high specificity, but the sensitivity of these tests was low. In many RA patients the occurrence of IgM-RF and anti-CCP antibodies was independent. Thus the optimal criterion proved to be the combination of IgM-RF > 40 or anti-CCP > 50, which yielded sensitivity of 55.4% and specificity of 96.7%.
  
  
  CONCLUSIONS
  The criterion IgM-RF > 40 or anti-CCP > 50 is able to predict the diagnosis of RA in early arthritis patients with high specificity and acceptable sensitivity. Anti-CCP testing combined with IgM-RF testing has additional value over IgM-RF testing alone in patients with early undifferentiated oligo and polyarthritis.
authors.affiliation: Jan van Breemen Instituut and the Department of Rheumatology, VU Medical Center, Amsterdam, The Netherlands.
authors.forename: Annemarie L M A
authors.initials: AL
authors.lastname: Jansen
authors.forename: Irene
authors.initials: I
authors.lastname: van der Horst-Bruinsma
authors.forename: Dirkjan
authors.initials: D
authors.lastname: van Schaardenburg
authors.forename: Rob J
authors.initials: RJ
authors.lastname: van de Stadt
authors.forename: Margret H M T
authors.initials: MH
authors.lastname: de Koning
authors.forename: Ben A C
authors.initials: BA
authors.lastname: Dijkmans
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000276:immunology*; D001323:Autoantibodies / Q000276:immunology*; D002956:Citrulline / Q000276:immunology*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010045:Outpatients; D010456:Peptides, Cyclic / Q000276:immunology; D012217:Rheumatoid Factor / Q000097:blood*; D012680:Sensitivity and Specificity
chemical_list: D001323:Autoantibodies; D010456:Peptides, Cyclic; D002956:Citrulline; D012217:Rheumatoid Factor