title: Role of anticyclic citrullinated peptide in the diagnosis of early rheumatoid factor-negative suspected rheumatoid arthritis: is it worthwhile to order the test?
abstract: BACKGROUND
  Anticyclic citrullinated peptide (anti-CCP) is a relatively new serologic marker, which has been proposed for use in the diagnosis of rheumatoid arthritis (RA) and is said to be a highly specific.
  
  
  OBJECTIVE
  The aim of the study was to evaluate the role of anti-CCP in a South Indian population of patients with suspected RA in the early stages when rheumatoid factor is negative and clinical presentation is atypical.
  
  
  METHODS
  Patients with early inflammatory arthritis who were rheumatoid factor-negative were investigated for anti-CCP. The patients were reviewed by a rheumatologist and, based on American College of Rheumatology criteria, were diagnosed with RA or another disease after a follow-up period of 3 to 6 months. The rheumatologist was blinded to the results of the anti-CCP. The sensitivity and specificity of anti-CCP was estimated in comparison to follow up and final clinical diagnosis. The anti-CCP was estimated by the enzyme-linked immunosorbent assay method using a commercially available kit (Euroimmune).
  
  
  RESULTS
  One hundred forty-three patients with a mean age of 47.1 years and a male to female ratio of 0.22:1 were recruited for the study. Thirty cases were positive for anti-CCP and 41 cases were finally diagnosed RA. Twenty-six of the 30 anti-CCP-positive patients were diagnosed with RA. Thus, the sensitivity of anti-CCP in our institution for the diagnosis of RA in the early stage in a group of rheumatoid factor-negative patients with atypical presentation was 63.4% with 36.6% false-negatives and the specificity was 96.1% with 3.9% false-positive cases. The positive predictive value of anti-CCP was 86.7% and the negative predictive value was 86.7%. Kappa statistic of agreement, chi McNemar test, indicated anti-CCP to be an efficient test in this study population.
  
  
  CONCLUSIONS
  Anti-CCP is a useful and highly specific but not absolutely specific or sensitive test to detect RA and supplements rheumatoid factor in the presence of a strong clinical suspicion.
authors.affiliation: Chanre Diagnostic Laboratory, Chanre Rheumatology & Immunology Center & Research, Bangalore.
authors.forename: Renuka
authors.initials: R
authors.lastname: Panchagnula
authors.forename: S R
authors.initials: SR
authors.lastname: Rajiv
authors.forename: J
authors.initials: J
authors.lastname: Prakash
authors.forename: S
authors.initials: S
authors.lastname: Chandrashekara
authors.forename: K P
authors.initials: KP
authors.lastname: Suresh
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000175:diagnosis* / Q000276:immunology; D001323:Autoantibodies / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D003937:Diagnosis, Differential; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000097:blood* / Q000276:immunology*; D013997:Time Factors
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide