Spectrum of biopsy proven renal diseases in Central China: a 10-year retrospective study based on 34,630 cases

Chronic kidney diseases have become a major issue worldwide. The spectrum of biopsy proven renal diseases differs between locations and changes over time. It is therefore essential to describe the local epidemiological trends and the prevalence of renal biopsy in various regions to shine new light on the pathogenesis of various renal diseases and provide a basis for further hypothesis-driven research. We retrospectively analyzed 34,630 hospitalized patients undergoing native renal biopsy between January 1, 2009 and December 31, 2018. Indications for renal biopsy and histological diagnosis were analyzed to describe the prevalence of renal biopsy, and changing prevalence between period 1 (2009–2013) and period 2 (2014–2018) were further analyzed. Nephrotic syndrome (NS) was the most common indication for biopsy. Membranous nephropathy (MN, 24.96%) and IgA nephropathy (IgAN, 24.09%) were the most common primary glomerulonephritis (PGN). MN was most common in adults, with IgAN more prevalent in children. Lupus nephritis (LN) was the most common secondary glomerulonephritis (SGN) in adults, while Henöch–Schönlein purpura nephritis (HSPN) in children. The prevalence of MN increased significantly and nearly doubled from period 1 (15.98%) to period 2 (30.81%) (P = 0.0004). The same trend appeared with membranoproliferative glomerulonephritis (MPGN), diabetic nephropathy (DN) and obesity-related glomerulopathy (ORG), while the frequencies of minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), LN and hepatitis B associated glomerulonephritis (HBV-GN) significantly decreased between the two intervals. NS was the most common indication for biopsy across all age groups and genders. MN has overtaken IgAN to become the most common PGN in adults, while IgAN was the most common PGN in children. LN was the most common SGN in adults, and HSPN the most common in children.


Study design and methods
In this cross-sectional retrospective study, we enrolled 34,839 patients who underwent native renal biopsy from our center, which covers more than 15 cities in Henan Province in Central China, during the period of January 1, 2009 to December 31, 2018. 209 cases with incomplete general data or insufficient renal tissue for evaluation were excluded; therefore, 34,630 eligible cases were included. Patients who had multiple biopsies, only the first biopsy was used in this study. All biopsy specimens were routinely processed and evaluated by light and immunofluorescence microscopy. Since 2014, electron microscopy (EM) was performed on nearly all biopsies. Before 2014, due to lack of EM facility in our center, EM was performed at an outside facility mainly on cases without which a definitive diagnosis cannot be reached (such as MCD, suspected hereditary and congenital renal disease and so on). Overall, 60.69% of the cohort were examined by EM. Congo red staining was performed in patients over 40 years old (48.34%). All specimens were stained with hematoxylin and eosin (H&E), periodic acid-Schiff (PAS), Masson trichrome, and methenamine silver-periodic acid for light microscopy. Immunofluorescence staining included IgG, IgM, IgA, C3, C4, C1q, fibrinogen, and both kappa and lambda light chains (except children ≤ 14 years old). In cases with positive IgG, IgG subclass staining was performed as well.
The clinical indications for biopsy were classified as follows: nephrotic syndrome (NS), nephritic syndrome, acute nephritic syndrome (ANS), rapidly progressive glomerulonephritis (RPGN), asymptomatic urinary abnormalities (AUA), acute kidney injury (AKI) and chronic kidney disease (CKD). The definition of various clinical syndromes was listed in Table 1.
Clinical and pathological diagnoses of all cases had been established by a consensus among experienced nephrologists and nephropathologists. The study protocol was approved by the Ethics Committee of The First Affiliated Hospital of Zhengzhou University. All methods were carried out in accordance with relevant guidelines and regulations. Informed consent was obtained from all subjects or, if subjects are under 18, from a parent and/ or legal guardian. www.nature.com/scientificreports/ Statistical analysis. SPSS software was used for statistical analysis and the values were expressed as mean ± SD. Paired means were analyzed using Student's two-tailed t-test. Statistically significant difference was set at P < 0.05, and highly significant difference was set at P < 0.01.  (Fig. 1a, b). Nephrotic syndrome was the most common clinical indication for renal biopsy, accounting for 51.80% of all cases, followed by nephritic syndrome (36.12%), CKD (7.80%), AKI (1.93%), RPGN (1.44%), AUA (0.64%), and ANS (0.26%). NS was the most common indication for biopsy across all age groups and in both genders, followed by nephritic syndrome. All clinical indications were noted in patients over 20 years of age except ANS, which mainly occurred in children (56.67%). The majority of AUA was seen in young patients, with 63.06% in the 20-39-year age group (Table 2 and Fig. 2a, b).     (Table 3). MN (24.96%) and IgAN (24.09%) were the leading diagnoses in PGN, followed by MCD (10.71%), FSGS (2.45%), MPGN (0.61%), postinfectious GN (0.51%) and C3 glomerulopathy (0.14%) including C3GN (44 cases) and dense deposit disease (DDD, 4 cases) ( Table 3).

Discussion
Currently, there are no contemporary large-scale renal biopsy studies addressing kidney disease epidemiology in Central China. Henan province, located in Central China, is one of the most populated provinces in China, with over 100 million people, and has among the highest prevalence of renal disease in China. As one of the largest kidney pathology centers in China (located in Zhengzhou, the capital of Henan province), we retrospectively analyzed 34,630 hospitalized patients residing in Henan province who underwent native renal biopsy in our Scientific RepoRtS | (2020) 10:10994 | https://doi.org/10.1038/s41598-020-67910-w www.nature.com/scientificreports/ center over the past 10 years to explore the epidemiology of kidney disease. This study provides for the first time a picture of the current spectrum of renal disease in this region, which can serve as a useful resource for making health policy decisions and hypothesis-driven research to conquer renal diseases. We identified primary GN as the leading pathological findings, followed by systemic/secondary GN (Table 3). A significant temporal shift in the epidemiology of many renal diseases over the past decade was noted. In adults, the prevalence of MN increased dramatically over the past decade. The frequency of MN increased from 10.77% in 2009 to 32.98% in 2018, and MN has overtaken IgAN as the most common PGN since 2015 (Fig. 4a). The prevalence nearly doubled from 2009-2013 (15.98%) to 2014-2018 (30.81%) (P = 0.0004) (Fig. 4b), which is consistent with previous studies from Northeast China 8 . The prevalence of MN has also increased significantly in India 12 and Brazil 13 , but has decreased in Japan 14 , Korea 15 , USA 16,17 , and UK 18 . It is suggested that the increased prevalence of MN in developing countries, including China, and its decrease in developed countries might be related to environmental exposures related to industrialization, as well as socioeconomic factors and geographical and genetic influences 7,19 . In fact, Xu et al. found long-term exposure to air pollution to be associated with increased risk of MN in China 20 . Since 2014, PLA2R staining has been done for 2,593 cases of MN, 84.65% (2,195 cases) of which were positive, which is similar to the findings previously reported (85%) 21 .
In our study, IgAN showed a gradually decreasing trend for the study duration, with 27.06% in 2009 and 21.07% in 2018, but there is no statistical significance between the two intervals (P = 0.1036) (Fig. 4a, b), and this phenomenon differs from other Asian countries. For instance, the relative frequency of IgAN has increased significantly in Korea 15    www.nature.com/scientificreports/ two intervals. Nephritic syndrome remained the most common clinical indication for biopsy in IgAN and had no significant changes (P = 0.6250) between the two intervals. NS, ANS, RPGN, and AKI had a mild decrease without statistical significance (P = 0.1137, 0.2161, 0.8093, and 0.6761, respectively) between the two intervals. MCD contributed 10.71% in our study, within the range seen in other areas of China (8.1-14.81%) 7,8,19,23,24 , but significantly higher than those previously reported in Central China (1.82%) by Xu et al. 22 . The frequency gradually decreased during the study period, with statistical significance between the two intervals (14.83% vs 8.03%, P = 0.0011) (Fig. 4a, b). These findings are consistent with previous studies by Zhu 7 . A gradually decreasing trend was shown, with statistical significance between the two intervals (3.38% vs 1.85%, P = 0.0084) (Fig. 4a, b) Immune complex-mediated MPGN without identifiable etiologies contributed 0.61% in our cohort. The frequency increased significantly between the two intervals (0.43% vs 0.72%, P = 0.0042) (Fig. 4a, b), which is opposite to the study by Xu et al. from Central China 22 and other Asian countries, such as Korea 15 .
In this study, postinfectious GN, all showed elevated anti-streptolysin O titers, represented 0.51% of the full cohort, which is lower than the previous report (7.5%) 25 . The change of frequency has no statistical significance between the two intervals (P = 0.2067). In our center, just few IgA dominant-infection-associated glomerulonephritis (15 cases) was diagnosed, and classified to the cohort of miscellaneous.
Recently, an increasing number of reports have emerged in regard to IgAN combined with other renal diseases 10,11,26,27 . In our study, MN combined with IgAN was diagnosed in 451 cases since 2010, with NS as the most common clinical indication (77.16%) for biopsy, followed by nephritic syndrome (22.39%) (Fig. 3). MCD www.nature.com/scientificreports/ combined with IgAN has been uncommonly reported, mostly in patients presenting with full NS who meet criteria for IgAN with only mild mesangial proliferation, in addition to diffuse foot process effacement without peripheral capillary wall immune complex deposits, reminiscent of MCD 11 . Since 2013, we have diagnosed 97 cases, mostly presenting with NS (94.85%), followed by nephritic syndrome (5.15%) (Fig. 3).
In adults, LN remains the most common SGN, although prevalence has significantly decreased over time, which is compatible with most studies 7,15,22,23,25,28 , but differs from the report from Northeast China which showed HSPN as the most common SGN followed by LN 8 . Additionally, a significant decrease in the prevalence of HBV-GN (MN pattern: 881 cases, MPGN pattern: 69 cases) was also observed from period 1 to period 2 (5.24% vs 1.12%, P = 0.0487)( Table 3 and Fig. 4c, d). This change is related to the widespread HBV vaccinations in China since 1992, leading to marked reduction in HBV infections 8,29 .
The prevalence of DN and ORG has gradually increased with statistical significance between the two intervals (1.68% vs 3.38%, P = 0.0098, 0.86% vs 1.65%, P = 0.0054, respectively) (Fig. 4c, d), similar to findings regarding DN reported by other centers in China 22,23 . A recent study estimated that high body mass index (BMI) was the leading individual-attributable factor for diabetes mellitus in China, responsible for 43.8 million cases, with a population attributable fraction of 46.8% in 2011 3,30 . Indeed, Chinese men and women ranked 60th and 41st, respectively, in terms of severe obesity in 1975, while both were ranked second globally by 2014 3,31 . DN and ORG are both potentially preventable through promoting healthy lifestyle choices and reducing obesity, which are topics that are at the forefront of current public health campaigns 4 .
TID represented 2.55% of the full cohort, with no significant change in prevalence over the past decade (Table 3), which is consistent with previous studies by Zhou et al. from East China 23 , but contrary to the findings reported by Su et al. from Northeast China 8 , in which the frequency of TID significantly increased. There was no significant change in the prevalence of AIN, ATN, CTIN, or light chain cast nephropathy between the two intervals (Fig. 4e, f).
The frequency of vascular diseases was 1.72% in our study, and there was no significant change in frequency for the study duration. The prevalence of both hypertensive nephrosclerosis and TMA had no significant changes between the two intervals ( Fig. 4g-h).
In our study, NS was the most common clinical indication for renal biopsy, followed by nephritic syndrome ( Table 2). These results are consistent with most previous reports 12, 28,35,36 , including those from several centers in China 7,8,19 , but not those from Japan (nephritic syndrome followed by NS) 37 , South Korea (AUA, followed by NS) 25 , and one report with a smaller number of cases from Central China (proteinuria and hematuria, followed by NS) 22 . Variation in renal biopsy policies and in diagnostic criteria of histopathological diagnoses may be the reasons of the above-mentioned discrepancies.
Central China has among the highest prevalence of renal disease in China, and this is the first large-scale epidemiological study of renal disease from this region. However, as a single-center study, the enrolled patients mostly came from Henan province, and may not represent the variety of regions in China and the Chinese population as a whole. Additionally, there may be bias for the enrolled patients who underwent renal biopsy due to variation in renal biopsy policies and in diagnostic criteria of histopathological diagnoses.
In summary, PGN was the most common pathological finding overall, and MN was the most common PGN in adults, while IgAN was the most common in children. LN was the most common SGN in adults, although the prevalence has significantly decreased over time, while HSPN was the most common SGN in children. DN and ORG tripled over the past decade. Together, these findings describe the local epidemiological trends and the prevalence of renal biopsies in Central China and provide a reference point for better understanding and prevention of renal disease.