The possible confounding influence of investigator-related preferences, available histological techniques, and healthcare systems on the frequencies and incidences of primary and secondary nephropathies was evaluated in this long-term observation. The observation time from 1983 to 2010 was divided in regard to the political regimes: a) prior to and after German reunification: German Democratic Republic (GDR, period 1 from 1983 to 1990)/Federal Republic of Germany (FRG, period 2 from 1990 to 2010); and the two heads of the division of nephrology, b) conductor 1 (1983 - 2006) and conductor 2 (2006 - 2010). 467 kidney biopsies at the University Hospital of Leipzig were included in our analysis. In period 1, due to the unavailability of immunofluorescence methods, mesangioproliferative glomerulonephritis (MesP) was the most dominating nephropathy. In period 2, IgA nephropathy (IgAN) was the most common nephropathy (17%). IgAN was followed by crescentic glomerulonephritis (13%), hypertensive nephropathy (10%), minimal-change disease, and membranous glomerulonephritis (each 9%). From period 1 to period 2, MesP/IgAN (62% to 16%), membranoproliferative glomerulonephritis and postinfectious glomerulonephritis decreased significantly (p < 0.05). IgAN decreased significantly (p < 0.05) from conductor 1 to conductor 2 (21% to 6%), while diabetic nephropathy significantly increased. Focal-segmental glomerulosclerosis (FSGS) had the highest incidence rate with 1.0, followed by IgAN with 0.8 (per 100,000 per year). In a nearly ethnically identical cohort, we have demonstrated that confounding factors, e.g., healthcare systems and preferences of conductors, have a strong influence - more than 10-fold variance - on frequency and incidence on the spectrum of nephropathies.
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