The American College of Rheumatology (ACR) 1987 criteria for rheumatoid arthritis (RA) can be applied in 2 formats, a standard "x/y" list and a decision tree. This study evaluated the performance of the decision tree compared with the list approach in the ascertainment of RA in subjects with new-onset inflammatory polyarthritis (IP) over the first 5 years of observation. Moreover, the use of clinical surrogates to substitute for missing rheumatoid factor (RF) and radiologic erosion data was assessed for validity and for its influence on the resulting RA prevalence estimates.
In this population-based prospective study, 848 subjects with new-onset IP were interviewed and examined at baseline, with followup at 1, 2, 3, and 5 years. RF and erosion status were determined at prespecified time points. The list criteria were applied cumulatively, while the decision tree was applied cross-sectionally using either data surrogates or the actual reported data. RA prevalence in the 848 subjects and agreement in classification between the 2 methods was assessed at each time point. The influence of using clinical surrogates on RA prevalence estimates at 5 years and the agreement between surrogate and real results were also analyzed.
At baseline, RA prevalence was higher using the decision tree compared with the list approach (63% versus 47%; P = 0.0001); by 5 years of followup, RA estimates were approximately equal (69% versus 72%) and agreement between the approaches was good (kappa = 0.67). The use of surrogates had little influence on RA prevalence at 5 years, although substitution of metacarpophalangeal joint swelling for erosion produced a higher RA prevalence estimate (78% versus 70%). Although there was only weak agreement between surrogate and real data, the use of the surrogate data provided good to very good agreement between the approaches in categorizing subjects as RA positive (kappa = 0.61-0.72).
Over 5 years, the 2 formats of the ACR criteria for RA performed similarly, with no important differences between them. The use of surrogates for missing radiologic and serologic data did not have any major influence on disease classification. Although the RA criteria were not originally derived from subjects with early disease in a population setting, this study shows that the use of the decision tree approach with the option of substituting clinical surrogates for missing laboratory data is an appropriate alternative to the conventional list approach.