#2011 Data from the single largest native kidney biopsy center in Croatia (1996–2023)

Abstract Background and Aims Epidemiologic data on biopsy-proven renal disease are of utmost importance for determining true incidence and prevalence of those relatively rare diseases. Our hospital native kidney biopsy database contains data on adult patients who had biopsy performed in our center from the year 1996 and is the largest in Croatia. The aim of this report was to review patients’ clinical and histological data from 1996 till the end of 2023. Method Demographic (age, gender) and clinical/laboratory (hypertension, eGFR according to CKD-EPI 2009 equation, urine sediment, 24-hours proteinuria) data were analyzed as well as indications for kidney biopsy and histological diagnoses. The indications were classified into: asymptomatic proteinuria and/or hematuria, nephrotic syndrome, acute or rapidly progressive nephritic syndrome and chronic nephritic syndrome (defined by KDIGO guidelines). Indications that didn't fit the criteria for these syndromes were classified as other. Every kidney biopsy was analyzed by light and immunofluorescent microscopy, while electron microscopy was performed in the majority of the patients. Results After exclusion of 119 patients with repeated kidney biopsy (4.94%), there were 2287 patients for analysis. Median age at biopsy was 50 years (interquartile range, IQR 38–63), the majority of patients were men (57.8%), and had hypertension (69.8%). Median eGFR was 54.7 ml/min/1.73 m2 (IQR 25.9–85.2), and median 24-hours proteinuria was 2.3 g (IQR 0.7–6.0). The most common indication for biopsy was nephrotic syndrome (34.7%), followed by asymptomatic proteinuria and/or hematuria (30.5%). The most common diagnoses overall were: IgA nephropathy (IgAN, 19.2%), followed by focal segmental glomerulosclerosis (FSGS, 14.9%) and membranous nephropathy (MN, 8.4%). The diagnostic category of FSGS included primary forms as well as secondary forms where it was the only histological finding. The most common secondary forms of kidney diseases were: diabetic nephropathy (5.7% overall), lupus nephritis (5.6%) and kidney diseases related to monoclonal gammopathies (4.1%). Compared to women, men had more often hypertension (73.5 vs. 64.7%, P < 0.001), higher 24-hour proteinuria (median 2.8 vs. 1.8 g, P < 0.001), and lower eGFR (median 49.94 vs. 60.85 ml/min/1.73 m2, P < 0.001). The most common indication for biopsy in men was nephrotic syndrome (36.3%), while in women it was asymptomatic proteinuria and/or hematuria (38.1%). The most common diagnoses in men were: IgAN, FSGS and MN (24.5, 14.9 and 9.2% respectively), and in women: FSGS, Alport spectrum disorders (including thin basement membrane nephropathy and Alport syndrome) and IgAN (13.9, 12.6 and 11.9% respectively). The most common diagnosis among patients with asymptomatic proteinuria and/or hematuria were IgAN and Alport spectrum disorders (26.1 and 20.8% respectively), among patients with acute/rapidly progressive nephritic syndrome the most common were ANCA-associated glomerulonephritis (GN) and IgAN (38.4 and 20.1% respectively) and among patients with nephrotic syndrome, MN and FSGS (21.0, 18.1% respectively). There were 468 older patients (age ≥ 65 years) in the database. They had more often hypertension (81.0 vs. 66.9%, P < 0.001), lower EGFR (median 27.52 vs. 62.63 ml/min/1.73 m2, P < 0.001) and higher 24-h proteinuria (median 3.68 vs. 2.06 g, P < 0.001). The most common indication for biopsy in this group was nephrotic syndrome, and the most common diagnoses were: ANCA-associated GN and MN (12.8 and 12.0% respectively). Conclusion The presented data should serve as a source for nephrologists and health care providers to stimulate new analysis and investigations and to improve prevention and treatment of biopsy-proven kidney diseases in Croatia and Europe through comparison with data from other registers. The data from the year 2019 onwards are also included into the Croatian national register of native kidney biopsies.