The validity of pathology codes for biopsy-confirmed kidney disease in the Danish National Patobank

Background. This study validates the application of Systematized Nomenclature of Medicine second edition( SNOMED II) codes used to describe medical kidney biopsies in Denmark in encoded form, aiming to support robust epidemiological research on the causes, treatments and prognosis of kidney diseases. Methods. Kidney biopsy reports from 1 January 1998 to 31 December 2018 were randomly extracted from the Danish National Patobank, using SNOMED codes. A 5% sample was selected, and nephrologists assessed the corresponding medical records, assigning each case the applied clinical diagnoses. Sensitivity, specificity, positive predictive values ( PPV) , negative predictive values and Cohen's kappa coefficient for the retrieved SNOMED codes were calculated. Results. A total of 613 kidney biopsies were included. The primary clinical disease groups were glomerular disease ( n = 368) , tubulointerstitial disease( n = 67) , renal vascular disease( n = 51) , diabetic nephropathy( n = 51) and various renal disorders( n = 40) . Several SNOMED codes were used to describe each clinical disease group and PPV for the combined SNOMED codes were high for glomerular disease( 94%) , diabetic nephropathy( 85%) and systemic diseases affecting the kidney( 96%) . Conversely, tubulointerstitial disease( 62%) , renal vascular disease( 60%) and other renal disorders( 17%) showed lower PPV. Conclusions. SNOMED codes have a high PPV for glomerular diseases, diabetic nephropathy and systemic diseases affecting the kidney, in which they could be applied for future epidemiological research.