Methodological challenges when comparing demographic and clinical characteristics of international observational registries.

OBJECTIVE: Comparisons of data from different registries can be helpful in understanding variations in many aspects of rheumatoid arthritis (RA). The study aim was to assess and improve the comparability of demographic, clinical, and comorbidity data from 5 international RA registries. METHODS: Using predefined definitions, 2 subsets of patients (main cohort and sub-cohort) from 5 international observational registries (CORRONA, SRR, NOAR, IORRA, and CORRONA International) were evaluated and compared. Patients with RA aged >18 years, and present in or recruited to the registry from January 1, 2000, were included in the main cohort. Patients from the main cohort with positive rheumatoid factor and/or erosive RA who had received ≥1 sDMARD, and switched to or added another DMARD, were included in the sub-cohort at time of treatment switch. RESULTS: Age and gender distributions were fairly similar across the registries. The percentage of patients with high DAS28 score varied between main cohorts (17.5% IORRA, 18.9% CORRONA, 24.7% NOAR, 27.7% CORRONA International, and 36.8% SRR), with IORRA, CORRONA, and CORRONA International including more prevalent cases of RA; the differences were smaller for the sub-cohort. Prevalence of comorbidities varied across registries (e.g., coronary artery disease ranging from 1.5% in IORRA to 7.9% in SRR), partly due to the way comorbidity data was captured and general cultural differences; the pattern was similar for the sub-cohorts. CONCLUSION: Despite different inclusion criteria for the individual RA registries, it is possible to improve the comparability and interpretability of differences across RA registries by applying well-defined cohort definitions. This article is protected by copyright. All rights reserved.