[Development and internal validation of case definitions for kidney disease in patients with diabetes based on routine data of statutory health insurance]

Diabetic kidney disease and renal replacement therapy are long-term complications of diabetes mellitus and significantly contribute to disease burden. The aim of the analysis was to develop case definitions for diabetic kidney complications in routine data as part of the diabetes surveillance and to internally validate them.Based on an age- and sex-stratified sample of persons covered by the Barmer health insurance, individuals with documented diabetes (E10-E14) were included and differentiated by type 1 (T1D) and type 2 diabetes (T2D). Case definitions were developed for persons with diabetic nephropathy (DNP; ICD: N08.3, E1x.2), chronic kidney disease (CKD; ICD: N18) and renal replacement therapy (RRT) with long-term dialysis (EBM: 40815-40819, 40823-40828 / OPS: 8-853, 8-854, 8-855, 8-857) or kidney transplantation (OPS: 5-555; EBM: 04561, 13601; ICD Z94.0). The temporal persistence of DNP and CKD was examined by considering different observation periods, and the internal validity was assessed using additional information from the data set for DNP, CKD, and RRT.In 2018, DNP was documented in 15.4% of individuals with diabetes (T1D: 18.3%; T2D: 15.2%), and CKD in 21.8% (T1D: 14.4%, T2D: 22.2%). Considering an observation period of five years (2014-2018), the prevalence estimates increased by 22 and 23%, respectively. RRT was documented in 7.5 per 1,000 individuals with diabetes. Internal validity assessment showed that 96.6% of DNP cases, 93.5% of CKD cases, and all RRT cases met at least one validation criterion.With high internal validity, and prevalence estimate consistent across age groups, the case definition of CKD can be considered suitable for use in surveillance. However, we assume that prevalence is underestimated when considering a 1-year period. For the depiction of RRT (kidney transplantation or long-term dialysis) via routine data, documentation of services must be employed.