Epidemiology of native kidney disease in Flanders: results from the FCGG kidney biopsy registry

Abstract

Background: The Flemish Collaborative Glomerulonephritis Group (FCGG) registry is the first population-based native kidney biopsy registry in Flanders, Belgium. In this first analysis, we report on patient demographics, frequency distribution and incidence rate of biopsied kidney disease in adults in Flanders.

Methods: From January 2017 to December 2019, a total of 2054 adult first native kidney biopsies were included. A 'double diagnostic coding' strategy was used, in which every biopsy sample received a histopathological and final clinical diagnosis. Frequency distribution and incidence rate of both diagnoses were reported and compared with other European registries.

Results: The median age at biopsy was 61.1 years (interquartile range, 46.1-71.7); male patients were more prevalent (62.1%) and biopsy incidence rate was 129.3 per million persons per year. Immunoglobulin A nephropathy was the most frequently diagnosed kidney disease (355 biopsies, 17.3% of total) with a similar frequency as in previously published European registries. The frequency of tubulointerstitial nephritis (220 biopsies, 10.7%) and diabetic kidney disease (154 biopsies, 7.5%) was remarkably higher, which may be attributed to changes in disease incidence as well as biopsy practices. Discordances between histopathological and final clinical diagnoses were noted and indicate areas for improvement in diagnostic coding systems.

Conclusions: The FCGG registry, with its 'double diagnostic coding' strategy, provides useful population-based epidemiological data on a large Western European population and allows subgroup selection for future research.

Keywords: biopsy; epidemiology; frequency; incidence; native kidney; observational; pathology; registry.

Graphical Abstract

Figure 1:

Flowchart of kidney biopsy selection for final analysis.

Figure 2:

Categorization of histopathological and final clinical coding systems in the FCGG registry.

Figure 3:

Demographics and biopsy rate of biopsied adult patients. (A) Biopsy rate according to age category in Flemish adult patients from 2017 to 2019. (B) Biopsy rate according to sex category in Flemish adult patients from 2017 to 2019. (C) Sex distribution in adult patients, shown for the total number of biopsies and for individual kidney diseases (ERA level 1, male proportion in blue, female proportion in red). AAV: ANCA-associated vasculitis and pauci-immune glomerulonephritis; Alp/TMD: Alport syndrome and thin basement membrane disease; AMY: amyloidosis; DKD: diabetic kidney disease; FSGS: focal segmental glomerulosclerosis; IgAN: IgA nephropathy; LN: lupus nephritis; MCD: minimal change disease; MN: membranous nephropathy; NScl: nephrosclerosis; TIN: tubulointerstitial nephritis; TMA: thrombotic microangiopathy.

Figure 4:

Final clinical diagnoses of biopsied adult patients per kidney tissue compartment. Final clinical diagnoses are categorized according to the most frequently affected kidney tissue compartment (ERA level 2).

Figure 5:

Most frequently biopsied kidney diseases in Flanders. The 10 most frequent final clinical diagnoses are shown (ERA level 1). Frequencies were calculated relative to the total number of adult biopsies (N = 2054). The nonspecific clinical categories ‘AKI/CKD, NOS’ (6.3%) and ‘glomerulopathy, NOS’ (3.7%) were omitted from the chart. AAV: ANCA-associated vasculitis and pauci-immune glomerulonephritis; AMY: amyloidosis; DKD: diabetic kidney disease; FSGS: focal segmental glomerulosclerosis; IgAN: IgA nephropathy; LN: lupus nephritis; MCD: minimal change disease; MN: membranous nephropathy; NScl: nephrosclerosis; TIN: tubulointerstitial nephritis.