title: Levels of anti-citrullinated protein antibodies and IgM rheumatoid factor are not associated with outcome in early arthritis patients: a cohort study.
abstract: BACKGROUND
  To investigate whether baseline levels of anti-citrullinated protein antibody (ACPA) or IgM rheumatoid factor (IgM-RF) and changes in the year thereafter are associated with disease activity, functional and radiographic outcome in early arthritis patients, and provide additional information over baseline autoantibody status.
  
  
  METHODS
  In 545 early arthritis patients ACPA and IgM-RF levels, disease activity (DAS28), the Health Assessment Questionnaire (HAQ) and Sharp/Van der Heijde Score (SHS) were assessed annually. Baseline status, levels and first-year changes of the autoantibodies were associated with these measures at the two-year follow-up and sub-analysed according to autoantibody status.
  
  
  RESULTS
  The mean age was 52.7 years, 69% was female, at baseline 56% was ACPA positive, 47% IgM-RF positive. At the two-year follow-up the mean DAS28 was 2.88, and the median HAQ and SHS were 0.38 and 1, respectively. At one year, ACPA and IgM-RF levels had decreased by 31% and 56%, respectively. A switch from negative to positive occurred in 2% for ACPA and 3% for IgM-RF. Positive ACPA and RF status were both associated with SHS at two years (P < 0.001), but baseline levels only showed a minor correlation of ACPA with DAS28 and HAQ at two years. Level changes were not associated with the outcome parameters.
  
  
  CONCLUSIONS
  Baseline levels and first-year changes of ACPA and IgM-RF are hardly associated with outcome after two years. Seroconversion seldom occurs. Therefore, it does not appear useful to repeat ACPA or IgM-RF measurements.
authors.affiliation: Jan van Breemen Institute, department of rheumatology, Dr, Jan van Breemenstraat 2, 1056 AB Amsterdam, The Netherlands.
authors.forename: Jennie
authors.initials: J
authors.lastname: Ursum
authors.forename: Wouter H
authors.initials: WH
authors.lastname: Bos
authors.forename: Nancy
authors.initials: N
authors.lastname: van Dillen
authors.forename: Ben Ac
authors.initials: BA
authors.lastname: Dijkmans
authors.forename: Dirkjan
authors.initials: D
authors.lastname: van Schaardenburg
mesh_terms: D018501:Antirheumatic Agents / Q000627:therapeutic use; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000188:drug therapy / Q000276:immunology; D001323:Autoantibodies / Q000097:blood* / Q000276:immunology; D001324:Autoantigens / Q000276:immunology / Q000378:metabolism; D002956:Citrulline / Q000378:metabolism; D015331:Cohort Studies; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007075:Immunoglobulin M / Q000097:blood / Q000276:immunology; D008297:Male; D008875:Middle Aged; D011506:Proteins / Q000276:immunology / Q000378:metabolism; D012217:Rheumatoid Factor / Q000097:blood* / Q000276:immunology; D012720:Severity of Illness Index; D016896:Treatment Outcome
chemical_list: D018501:Antirheumatic Agents; D001323:Autoantibodies; D001324:Autoantigens; D007075:Immunoglobulin M; D011506:Proteins; D002956:Citrulline; D012217:Rheumatoid Factor