To investigate the perception of values of individual core set measures by rheumatologists, and how it differs across measures and across physicians.
We designed a survey in which 44 international expert rheumatologists explicitly marked positions on the scales of seven core-set measures that in their opinion corresponded to cut-points between remission, low, moderate and high disease activity. The measures comprised swollen and tender joint counts (SJC, TJC), CRP, ESR, patient and evaluator global assessments of activity (PGA, EGA), and the Health Assessment Questionnaire Disability Index (HAQ).
The interpretation of measures across physicians was most consistent for ESR and PGA, while for CRP and joint counts there was most variation. Joint counts and CRP implied active disease at lower relative values (using normalized scales) than did PGA, EGA or ESR (P < 0.01 for most comparisons; Bonferroni-adjusted Wilcoxon signed rank test), and most physicians tended to tolerate higher numbers of tender joints than swollen joints to define similar levels of disease activity. Given these cut-points, more RA patients in a typical cross-sectional cohort would be regarded as being in remission according to joint counts (SJC, 35%; TJC, 55%) than to global scores (PGA, 18%; EGA, 9%), and fewer patients would be regarded as being in remission by physician-derived or laboratory measures than by patient-derived ones.
These data give insights into the integrative process of activity evaluation and will be informative for future survey designs, studies using physician opinion as the gold standard for criterion validity of disease activity, and allow 'activity mapping' of values on different scales based on expert opinion.