Trends in biopsy-confirmed kidney disease in the adult population of Central Poland: a single-region cohort of 13-year duration (2011–2023)

INTRODUCTION: Demographic, socioeconomic and environmental factors, including infections, vaccination and healthcare availability, may influence the spectrum of renal diseases. OBJECTIVES: This study examines trends in biopsy-confirmed kidney disease in adult Polish population (2011-2023), with emphasis on shifts during and after the COVID-19 pandemic. PATIENTS AND METHODS: We retrospectively analyzed 1,662 first native kidney biopsies performed in residents of the Lodz voivodeship (population: 2 million). Clinical and histopathological data were stratified by age, sex, and time period (pre-COVID, COVID, post-COVID) and compared with those reported by the same center in 1990-2010. RESULTS: Between 2011 and 2023, biopsy frequency increased from 43.9 to 102.2 per million population, with a temporary decline during COVID and a significant rise afterwards. The proportion of older patients increased, while nephrotic-range proteinuria became a less common biopsy indication. During COVID, patients presented with poorer renal function, and had higher rates of acute kidney disease. IgA nephropathy (IgAN) was the most frequent diagnosis (17.4%), with its proportion increasing during and after COVID, followed by focal segmental glomerulosclerosis (FSGS, 16.3%), membranous nephropathy (9.4%) and diabetic kidney disease (DKD, 8.0%). Minimal change disease frequency declined, other nephropathies remained stable, and a relative rise in tubulointerstitial disorders was observed. Compared with 1990-2010, the annual number of biopsies more than tripled, with a markedly older patient population and increased frequencies of FSGS, DKD and crescentic glomerulonephritis or necrotizing vasculitis. CONCLUSIONS: Over three decades, biopsy frequency in the Lodz Voivodeship has increased, particularly among older adults, with IgAN becoming the most common diagnosis.