Insights from native kidney biopsies: a step towards establishing a renal biopsies database in Latvia

Background and Aims
Percutaneous kidney biopsy is a cornerstone diagnostic procedure for the identification and characterization of kidney diseases, particularly glomerulonephritis, and for understanding their underlying pathophysiological mechanisms. However, the absence of comprehensive data on kidney disease patterns in Latvia hampers progress in disease management and population-level trend monitoring. This study presents an analysis of native kidney biopsy findings collected at Pauls Stradiņš Clinical University Hospital (PSCUH) from 2013 to 2024, in collaboration with the National Centre of Pathology in Vilnius.

Method
A retrospective analysis was conducted on 1752 patients undergoing percutaneous kidney biopsy, excluding transplant recipients and donors, leaving a cohort of 1002 patients. 34 biopsies were excluded due to insufficient biopsy material, 968 native kidney biopsies diagnosis were analyzed. Patients were categorized into four age groups: 18–44 years, 45–64 years, 65–74 years, and >74 years. The total number of case biopsies from 2013 through 2024 was used to calculate incidence rates, expressed as biopsies per million individuals per year (p.m.p./year). Since our center performs about 85% of all adult kidney biopsies nationwide, the official population counts at the beginning of each year were reduced by 15% in the denominator, ensuring the calculated rates accurately reflect the coverage of our kidney biopsies database.
Analyses were performed using IBM SPSS Statistics version 29.

Results
The incidence rate of Latvian adults undergoing first kidney biopsy was 58.3 p.m.p./year. The cohort's median age was 52 years, with 53.5% of biopsies on males and 46.5% on females. Yearly distribution of kidney biopsies ranged from 3.4% in 2013 to 14.1% in 2023 and 12.3% in 2024. Most biopsies were performed on patients aged 18–44 years (37.5%) and 45–64 years (37.9%), followed by 15.9% in those aged 65–74 years and 8.7% in individuals older than 74 years.
IgA nephropathy (IgAN) was the most common (23.3%), followed by rapidly progressive glomerulonephritis (RPGN) (15.0%), membranoproliferative glomerulonephritis (MPGN) (7.6%), focal segmental glomerulosclerosis (FSGS) (7.2%), lupus nephritis (5.9%), amyloidosis (6.5%), minimal change disease (MCD) (4.8%), and acute tubulointerstitial necrosis/acute tubular necrosis (ATIN/ATN) (7.5%). Other diagnoses included thrombotic microangiopathy/hemolytic uremic syndrome (TMA/HUS) (3.4%), diabetic nephropathy (DN) (3.4%), multiple myeloma (MM) (1.5%), hereditary interstitial nephritis (HIN) (1.0%), Alport syndrome (Alp)/Primary basement membrane syndrome (PBMS) (2.4%), and non-IgA mesangioproliferative glomerulonephritis (non-IgA MPGN) (1.7%).
A higher male predominance was noted for IgAN (9:5) and membranous GN (3:2), while female predominance was seen in lupus nephritis (1:10), Alp/PBMS (1:5), and MM (3:5) (Fig. 1).
Regarding age, IgAN prevailed in younger adults aged 18–44 (37.0%), while RPGN dominated in older adults aged ≥65 (21.6%), particularly those over 74 years (26.5%). Amyloidosis and ATIN/ATN showed a progressive increase in frequency with age, rising from 2.7% in the 18–44 age group to 13.3% for ATIN/ATN and 14.5% for amyloidosis in the >74 age group (Table 1).

Conclusion
This single-center study offers the most extensive biopsy-confirmed overview of kidney disease patterns at PSCUH to date, demonstrating a pronounced prevalence of IgAN overall and highlighting notable gender and age-related trends. The data also reveal rising rates of RPGN in older cohorts. These findings emphasize the need for a comprehensive, nationwide renal biopsies database in Latvia to advance epidemiological insights, optimize clinical management, and unify future research efforts.