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Table 3 Odds ratios for rheumatoid arthritis by anticitrullinated peptide autoantibody positivity and presence of HLA-SE a

From: Anti-citrullinated peptide autoantibodies, human leukocyte antigen shared epitope and risk of future rheumatoid arthritis: a nested case–control study

  ACPA-negative ACPA-positive  
Parameter Cases (N = 36) Controls (N = 268) OR (95% CI) Cases (N = 27) Controls (N = 15) OR (95% CI) OR (95% CI) for ACPA within strata of HLA-SE
HLA-SE absent 17 153 1.0 (ref) 6 8 7.7 (2.2 to 27.5) 7.7 (2.2 to 27.5)
       P = 0.002 P = 0.002
HLA-SE present 19 115 1.4 (0.7 to 2.9) 21 7 33.3 (11.1 to 99.6) 23.8 (7.9 to 71.8)
    P = 0.38    P < 0.0001 P < 0.0001
OR (95% CI) for HLA-SE present    1.4 (0.7 to 2.9)    4.3 (1.0 to 18.6)  
within strata of ACPA    P = 0.38    P = 0.05  
  1. aACPA: anticitrullinated antibody, CI: confidence interval, HLA-SE: human leukocyte antigen shared epitope, OR, odds ratio, ref: reference value. Measure of effect modification on the additive scale: Synergy Index = 4.5 (95% CI = 0.9 to 21.6; P = 0.06). Measure of effect modification on the multiplicative scale: ratio of odds ratios = 3.1 (95% CI = 0.6 to 15.8; P = 0.18). ORs estimated by logistic regression models adjusted for matching factors and age at blood draw, alcohol intake, body mass index, regularity of menses and pack-years of smoking. Restricted to cases with blood draw less than 5 years before diagnosis (cases = 63, controls = 283) in the Nurses’ Health Study and Nurses’ Health Study II.