Clinicopathological characteristics and disease chronicity in native kidney biopsies in Flanders

Abstract

Background: The Flemish Collaborative Glomerulonephritis Group (FCGG) registry provides complete population data on kidney disease epidemiology in the region of Flanders (Belgium), as it captures all native kidney biopsies performed in its population of 6.5 million inhabitants.

Methods: From 2017 until 2019, 2054 adult kidney biopsies were included from 26 nephrology centers (one biopsy per patient). Data on nephrotic and nephritic syndrome were available in 1992 and 2026 biopsies, respectively. In a subgroup of 898 biopsies containing ≥10 glomeruli from 2018 to 2019, disease chronicity was graded using the Mayo Clinic Chronicity Score (MCCS). The association between clinical variables and MCCS was determined using simple and multiple linear regression models.

Results: Nephrotic syndrome (present in 378 patients, 19.0%) was most frequently caused by minimal change disease in younger patients (18-44 years), membranous nephropathy in older patients (45-74 years) and amyloidosis in the elderly (>75 years). Nephritic syndrome (present in 421 patients, 20.8%) was most frequently caused by immunoglobulin A nephropathy (IgAN) in younger patients (18-64 years) and ANCA-associated vasculitis (AAV) in older patients (>64 years). AAV and IgAN were the most frequent underlying diagnoses in biopsies in which crescents were identified. In multivariable analysis, acute and chronic kidney disease and diagnoses of diabetic kidney disease, nephrosclerosis and hyperoxaluria/hypercalcemic nephropathy were associated with the highest MCCS increases.

Conclusions: The FCGG registry validates data from previous Western European registries and provides a snapshot of disease chronicity in the whole biopsied Flemish population.

Keywords: MCCS; chronicity; epidemiology; kidney biopsy; registry.

Graphical Abstract

Figure 1:

Flowchart of kidney biopsy selection for final analysis. *Based on ZIP-codes; ^†repeat biopsies were excluded, unless the first biopsy did not yield a diagnosis and a repeat biopsy was performed within the following 4 months, in which case the repeat biopsy was retained and the first biopsy excluded; ^‡for analysis of the MCCS, biopsies from 2017 were excluded, as this score was only introduced by Sethi et al. in 2017 [4]; ^§37 biopsies with no info on glomeruli, 397 biopsies with 0 to 9 glomeruli.

Figure 2:

Most frequent diagnoses in patients with NS according to age and sex category. The top five most frequent nephrological diagnoses (ERA level 1) are shown per age category in adult nephrotic males [(A), N = 230] and adult nephrotic females [(B), N = 148]. Disease proportions (%) were calculated in every age category separately. AMY: amyloidosis.

Figure 3:

Most frequent diagnoses in patients with nephritic syndrome according to age and sex category. The top five most frequent nephrological diagnoses (ERA level 1) are shown per age category in adult nephritic males [(A), N = 284] and adult nephritic females [(B), N = 137]. Disease proportions (%) were calculated in every age category separately. The non-specific nephrological diagnosis ‘AKI/CKD, NOS’ was omitted from the figure, and can be found in Supplementary data, Tables S6 and S7. AAV: ANCA-associated vasculitis and pauci-immune glomerulonephritis; ATN: acute tubular necrosis; A-GBM: anti-glomerular basement membrane nephritis; GP: glomerulopathy, not otherwise specified; NScl: nephrosclerosis; TMA: thrombotic microangiopathy; Vasc: ANCA-negative systemic vasculitis excluding IgA vasculitis.

Figure 4:

Etiologies most frequently associated with a crescentic pattern of kidney injury. The top six nephrological diagnoses (ERA level 1) of biopsies with a crescentic pattern of kidney injury are shown. The bar chart shows the absolute number of biopsies with crescents (blue bar), biopsies without crescents (grey bar) and total number of biopsies per disease (annotation above bar). The table shows the absolute number and proportion (%) of biopsies with a crescentic pattern of injury. AAV: ANCA-associated vasculitis and pauci-immune glomerulonephritis; A-GBM: anti-glomerular basement membrane nephritis; Vasc: ANCA-negative systemic vasculitis excluding IgA vasculitis.

Figure 5:

MCCS in adult biopsies. Chronicity grade (MCCS) in adult biopsies in Flanders (2018–19, ≥10 glomeruli), ‘total’ refers to the absolute number of biopsies in the subgroups: (A) overall chronicity (N = 898); (B) chronicity according to most frequently diagnosed kidney diseases (ERA level 1 shown, N = 670); (C) chronicity according to sex category (N = 898); (D) chronicity according to age category (N = 898); (E) chronicity according to kidney injury (N = 897; one biopsy with no data on kidney function excluded); (F) chronicity according to proteinuria, UPCR (g/g) or 24 h collection (g/24 h) (N = 891; seven biopsies with no data on proteinuria excluded). AAV: ANCA-associated vasculitis and pauci-immune glomerulonephritis; AMY: amyloidosis; NScl: nephrosclerosis.