Use cases of registry-based randomized controlled trials—A review of the registries' contributions and constraints

Registry-based randomized controlled trials (RRCTs) can combine the advantages of registries with those of randomization. This review aimed to expand the current knowledge on RRCT utilization and implementation by providing a comprehensive overview of RRCT use cases. A targeted literature search was conducted through July 2023 to identify articles on RRCTs. Information regarding the RRCT characteristics, their utilization, and the registries' contributions and the constraints faced was extracted. Descriptive statistics were used. We identified 102 RRCTs in 110 publications. RRCTs were mostly performed for the assessment of medical devices or surgical/clinical procedures (n = 45), followed by drugs (n = 30). More than half of the RRCTs were conducted in the Nordic countries (n = 58) and the most used registry types were health service registries/administrative health data (n = 63), followed by disease registries (n = 46). Approximately half of the RRCTs (n = 53) utilized additional data sources aside from registry data. The contribution of a registry to the RRCT was mostly for data collection and study follow-up (n = 90–92), followed by patient recruitment (n = 56–61), and randomization (n = 28–38), with varying levels of transparency in reporting. We collated author-reported constraints related to the used registries into four overarching themes, that is, data availability and completeness, data quality, representativeness, and registry infrastructure and accessibility. This review shows that RRCTs are already used in different domains and geographic regions. Guidelines on structured and transparent reporting of RRCT methods and the optimal use are, however, needed to inform decision-making by health authorities and to reach their full potential.