Table 3

Incidence of RA and RF findings in blood samples from 1996

Increased RF isotypes in 1996 blood sampleDevelopment of RA during the study period
NumberFollow up period (mean)Annual incidence (95% confidence intervals)
Group 1: No RF isotype (n=36)0 (0%)16.10% (0, 0.6)
Group 2: One RF isotype (n=30) *1 (3.3%)16.80.2% (0.01, 1.04)
Group 3: Two or three RF istotypes (n=54) 6 (11.1%)16.70.67% (0.25, 1.36)
  • Group 1 versus groups 2 and 3: p=0.074. Groups 1 and 2 versus group 3: p=0.045. *Isolated IgM RF. Five of these patients had two or three isotypes increased in the original blood sample. The approximate annual RA incidence and 95% confidence intervals in Finnish adults (⩾16 years) was 0.029 (0.025, 0.032).6