General data characteristics
retinopathy, diabetes complications, diabetes, albuminuria
RETINOPATHY, DIABETES
The missingness of data in the NDR with respect to EHRs was overall quite substantial; around 45% for creatinine and albuminuria, 33% for foot-at-risk grade, while only 13% for retinopathy status. Corresponding retinopathy grades were only available for 43% of all retinopathy entries but increased during the observational period, probably reflecting increasing awareness of the variable since its recent introduction in 2018. Creatinine and UACR may be obtained for reasons other than routine surveillance of diabetes complications by other health care units that do not report to the NDR. This is far less likely regarding foot examinations and highly implausible regarding fundus examinations. Moreover, diagnosis of albuminuria is often, and should be, a congregated assessment based on several repeated measurements. Previous measurements that have not coincided with the reporting of the albuminuria grade may therefore have been factored into the assessment notwithstanding the absence of a temporal association. Human errors in the documentation or transfer of EHR data or patient objection to data transfer may also explain some data loss to the NDR. Importantly, routines regarding frequency, completeness and method of reporting to the NDR differ among health care providers. For example, around one-third of all health care units still employs manual reporting of NDR data and automated data extraction, when implemented, is usually limited to the last available data for each variable. Obviously, a less selective automated extraction process, standardized and employed by all health care providers would overcome many potential sources of data loss. However, such a procedure may have ethical and legal issues relating to personal integrity.Notwithstanding possible causes of the observed missingness, there were no substantial numerical or proportional differences between missing and reported data, suggesting that neither the current results, nor the reliability of future results from the SMARTEST study appear to be at risk of marked influence from systematic, non-random loss of real-world data. Taken together, the resulting reporting rate for each investigated variable in the NDR seems adequate, both for the primary purpose of monitoring the national quality of diabetes care as well as for the applicable use as source data in observational and interventional clinical studies.