Table 5 Duration of preclinical rheumatoid factor positivity for all subjects by age-at-diagnosis*
Age at time of diagnosis of RA(years)NoDuration (years) of antibody positivity before diagnosis Median (95% CI)†Univariate hazard ratios (95% CI; p value)Adjusted hazard ratios (95% CI; p value)‡
20–29113.3 (2.3 to 4.7)Referent groupReferent group
30–39165.5 (2.8 to 11.1)0.34 (0.12 to 0.98; p = 0.04)0.40 (0.12 to 1.35; p = 0.14)
40–49148.4 (6.2 to 11.4)0.20 (0.06 to 0.61; p<0.01)0.29 (0.08 to 1.09; p = 0.08)
50+68.6 (3.7 to 20.0)0.18 (0.04 to 0.88; p = 0.03)0.14 (0.02 to 0.83; p = 0.04)
  • *Subjects included are those with preclinical RF positivity as determined by single RF cut-off point (>15.2 IU/ml).

  • †Determined from univariate analysis. For age group 50+, the earliest 95% confidence interval (20.0 years) is outside the range of the data. This is because of the small sample size and large numbers of subjects in this group with their earliest preclinical sample positive for RF. ‡Hazard ratios (HRs) are reported from survival models adjusted for gender, race and duration of preclinical samples available. An HR <1 indicates that the duration of antibody positivity is longer in the older age group than in the referent group of 20–29-year-olds.

  • RA, rheumatoid arthritis; RF, rheumatoid factor.