Strengths and limitations
diabetes
EVENT, COMPLICATION, EVENTS, TYPE 2 DIABETES, COMPLICATIONS, DIABETES
This is the first attempt to validate microvascular complication variables of the NDR. We have studied a large population with a long combined observational period. The extraction of EHR data has been systematic and has occurred independently of NDR data by independent health care staff with no self-interest in the outcome of the study.There are however some important limitations that need to be addressed. First, many participants did not have unique NDR entries after randomization and accordingly, the number of events for validation were few. Following inclusion in the SMARTEST study, the study participant’s regular care provider is notified regarding study involvement and is actively encouraged to report to the NDR. Thus, there is no considerable risk that this sparsity of NDR entries after randomization would result in an overestimation of the agreement between corresponding data from the two sources. Regarding agreement of event fulfilment, we recognize the need for further validation at a later stage of the SMARTEST study. However, it seems likely that discrepancies between the two sources would be expected to diminish rather than enhance with prolonged follow-up time and accumulation of data. Second, some EHR data may have been overlooked due to complicated structure of the EHRs. There are also some private care providers whose EHRs are difficult to access for external healthcare personnel. Third, the cohort in this study was limited to participants residing in three out of twenty-one Swedish health care regions, amounting to approximately one third of the SMARTEST study population that had been recruited by the time the current EHR extraction was terminated. Although this selected cohort was highly representative of the nationwide SMARTEST population in terms of clinical characteristics,Regardless of the limitations it is likely that the validity of NDR’s microvascular complication data would be similar across Swedish primary care for type 2 diabetes. Importantly, a main aim of this study was to address whether the NDR would provide appropriate data to collect outcome events of microvascular complications in the specific context of a register-based randomized controlled trial. We find that the NDR is a robust and valid data source for this purpose. Nonetheless, further research is warranted, for example to address the validity of register data of long-term trajectories of diabetes complications. We hope that this study may serve as an example for validation of register data that may be extended to other local and national health registers that are employed both for monitoring of health care quality and for scientific purposes.