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Table 1 Proportion of cases (n = 284) with elevation on the research ACPA and commercial CCP2 assays on blood bank prior to the index date of clinical RA diagnosis in the Nurses’ Health Studies

From: Asthma and elevation of anti-citrullinated protein antibodies prior to the onset of rheumatoid arthritis

 Proportion of pre-RA cases (n = 284)
Research ACPA assay results
 Elevateda research ACPA by targeted protein, %
  Anti-cit-apolipoprotein A2.8
  Anti-cit-apolipoprotein E8.5
  Anti-cit-biglycan8.5
  Anti-cit-clusterin11.7
  Anti-cit-enolase6.4
  Anti-cit-fibrinogen19.5
  Anti-cit-fibronectin7.8
  Anti-cit-filaggrin8.9
  Anti-cit-histone 2A12.8
  Anti-cit-histone 2B8.9
  Anti-cit-vimentin14.9
 CCP (research)15.6
 Any research ACPA+ or CCP+ (sensitive), %30.1
 ≥2 research ACPA+ or CCP+ (specific), %20.2
Commercial CCP2 assay results
 CCP2 >3 units/mL (sensitive cutpoint), %30.4
 CCP2 >5 units/mL (clinical cutpoint), %23.8
Definitions of ACPA positivity
 Primary/sensitive: any research ACPA+ or CCP2 >3 units/mL, %33.8
 Secondary/specific: ≥2 research ACPA+ or CCP2 >5 units/mL, %21.1
  1. The research ACPA assay was performed on a total of n = 1128 RA cases and matched controls. The commercial CCP2 assay was performed on a total of n = 450 RA cases and matched controls
  2. ACPA anti-citrullinated protein antibodies (research test), CCP2 second-generation cyclic citrullinated peptide (commercial test for research purposes), RA rheumatoid arthritis
  3. aElevated ACPA was defined as >99th percentile of the control distribution for each cohort (NHS or NHSII). Some of the targeted proteins were tested for two or more epitopes on the research ACPA assay. Separate cutpoints were determined for each batch