Objectives To identify cross-registrations (ie, registrations of the same trial in different registries) among clinical trials affiliated with German University Medical Centres (UMCs) and to describe how these cross-registrations are linked. To determine the consistency of key information across registrations of the same trial.
Design Observational cross-sectional study. Setting Registry-based study of clinical trials affiliated with German UMCs.
Participants 2895 interventional trials affiliated with German UMCs, registered on ClinicalTrials.gov or the German Clinical Trials Register (DRKS) and completed between 2009 and 2017. Main outcome measures Number of potential cross-registrations involving the EU Clinical Trials Register (EUCTR) and the type of linkage between these cross-registrations.
In a manually validated subset, consistency across registry entries of the same trial was assessed for prospective registration, recruitment status, completion date and availability of summary results. Results We identified 625 potential EUCTR cross-registrations.
The majority of potential cross-registrations (n=470; 75%) were linked through a trial registration number (TRN) in at least one of the registries. Only 109 (17%) were linked through a TRN in both registries.
To quantify registrations of the same interventional trial across different public registries (cross-registrations) for trials affiliated with German university medical centres (UMCs) and to characterize how those duplicate entries are connected and whether key metadata are consistent across them.
The study focussed on trials registered on ClinicalTrials.gov or the German Clinical Trials Register (DRKS) that completed between 2009 and 2017.
Observational, cross-sectional, registry-based analysis of 2,895 interventional trials with German UMC affiliation.
The analysis targeted potential links to the EU Clinical Trials Register (EUCTR) and assessed how cross-registrations were identified (e.g., trial registration numbers, title matching, citation in publications).
A manually validated subsample evaluated concordance of selected registry fields.
Investigators detected 625 candidate cross-registrations involving EUCTR.
Most candidates (470/625; 75%) were connected by the presence of a trial registration number (TRN) in at least one paired registry entry.
Only a minority (109/625; 17%) had a TRN present in both registries.
Title-based matching and presence of TRNs within trial result publications provided an additional 155 (25%) candidate links that were not captured by reciprocal TRN entries.
In a manually confirmed sample of 228 EUCTR cross-registrations, registry pairs showed incomplete agreement on core items.
Overall recruitment status was the same across paired entries for 85% (95% CI 80% to 89%; n=189) of confirmed matches, whereas completion dates agreed for 50% (95% CI 43% to 57%; n=92).
The EUCTR entry was the principal source for availability of summary results and included both structured tabular results and other formats.
Cross-registrations were common among the examined UMC-affiliated trials but frequently lacked robust inter-registry linking and showed inconsistent metadata between entries.
In settings such as Germany, where multiple registrations per trial occur frequently, unrecognized or poorly linked duplicates can alter assessments of registration completeness and results reporting.
The report does not provide outcomes beyond registry comparisons and does not address causes of discrepancies.