In our country, there is a long tradition of designing and maintaining records of the most prevalent kidney diseases such as glomerulonephritis (GN) and pathologies diagnosed by kidney biopsy. The studies on the epidemiology of biopsy kidney diseases in Spain, especially glomerular pathologies, was started in 1986 when the decrease in the incidence of membranoproliferative GN (MPGN) was independently described in two hospitals in Madrid.1,2 At that time, a publication in the journal Nefrología insisted on the need to join efforts to create study groups with the purpose of obtaining consistent and reliable multicenter data.3 Shortly after, in 1987, the first reports were published, both in the child population (1364 cases)4 and in the adult population (8545 cases),5,6 including kidney biopsies performed between 1970 and 1986. These publications, made by the SEN Study Group, mark the beginning of continued and productive work at the national level, a fact that was favorably commented on and encouraged by the then Director of the Nephrology Journal.7 A few years later, in 1990, a multicenter study was published, including 2123 kidney biopsies, carried out in 1987 and 1988, which consolidated the so-called "Spanish Registry of Glomerulonephritis (REGN)".8 Based on this registry there were several publications in the 90 s, reporting the results of kidney biopsies nationwide, with a significant percentage of participation by the Nephrology Services or Units of the entire country.9–15 In 1994, there were two new features introduced in data collection: a) filling individualized information of each patient to facilitate statistical processing and b) inclusion of non-glomerular pathology. With the information collected with a record for each renal biopsy, the first publication was made in Nephrology Dialysis and Transplantation in 2002,16 which had a high impact. In summary, 23 manuscripts have been published4,8–27: 12 in Nefrologia4,8,10–15,25 and 11 in other international journals16,26,27 (el numero de publicaciones no se corresponde con el numero de referencias). The reliability of the registry was demonstrated by the publication of detailed information about the incidence and prevalence of the different renal histological forms,6,8,10–13,15,16,25 as well as its correlations with the clinical expression,18 both in the child4 and in the elderly.14,20 In addition, certain clinical syndromes such as: acute renal failure,19 hematuria26 and nephrotic syndrome9 have been studied in depth. Various renal entities have been analyzed, such as IgA nephropathy,27 extracapillary GN,24 membranoproliferative GN,4,5,17 lupus nephritis,21 amyloidosis23 and acute tubulointerstitial nephritis.22 Since 1988 these data have been presented in the session of Registries at the annual congresses of the SEN, downloadable from the SEN website.28 To facilitate participation, for about 15 years, data has been sent electronically through the SEN website. As a last novelty, there has been stablished a link to send biopsy material to the SEN Biobank (https://www.senefro.org/modules.php?name=webstructure&idwebstructure=30) with the objective to collaborate with applied research using techniques of molecular biology and precision medicine.

With these information, it is confirmed that REGN is one of the largest and most reliable registries worldwide, since the mentioned manuscripts are included among the references of the research dealing with the epidemiology of the kidney biopsy diseases.

It is well known that kidney disease registries provide key information to be applied in clinical practice since it provides knowledge of the most frequent pathologies with real data on their incidence and prevalence,29 it facilitates the implementation of prevention and treatment protocols, as well as serving as the basis for multicenter clinical studies and trials. One of the fundamental points in of a registry is collaboration nationwide, with a form of data entry previously agreed,31 and a uniform policy of indication of renal biopsy32,33; the information obtained helps to answer unresolved questions about prevention and treatment of kidney diseases.34 As discussed in a previous publication, these were the reasons for the generation and development of the REGN.35 Another reason for having a registry of biopsied kidney diseases is that many pathologies, especially glomerular diseases, can only be diagnosed with certainty by doing a renal biopsy.30 A good example of this is the value of renal biopsy in acute renal failure36 or the study of glomerular pathology in elderly patients.37–39 Finally, the information provided with the registry may contribute to assess the overload that these diseases have on the health system due to the number of hospitalizations, progression towards advanced renal failure and deaths.40,41

Studies from a single center give relevant but insufficient information. However, a number of studies carried out in a single reference center have been published, such as studies from in Springfield and Minnesota in the US,42,43 Colombia,44 Ireland,45 Helsinki,46 Belgium,47 Germany,48,49 Porto (Portugal),50 Macedonia,51 Serbia,52 Poland,53 India,54 Japan,55 China,56 Korea,57 Thailand,58,59 Egypt,60,61 South Africa,62 South Asia63, Pakistan.64 In addition, local data have been published about certain renal syndromes, such as nephrotic syndrome in Chicago,65 China66 and Pakistan,67 acute kidney failure in Chicago68 and India69 and urinary disorders in Serbia.70 And also about specific entities as referents about the IgA N in Kentucky and in 24 states of the South and Midwest of USA,71,72 Focal Segmental glomerulosclerosis (FSG) in USA73,74 and Brazil,75 primary GN in Sao Paulo (Brazil)76 and UK,77 membranous nephropathy in UK,78 renal vasculitis in Norfolk (UK),79 extracapillary GN-pauci immune in Stockholm80 and Estonia,81 and thin basement membrane in Limburg (Netherlands).82 Finally, some studies have focused on certain age groups such as the child population in China83 and South Asia63 or in patients ≥ 60 years in Chicago,68 ≥ 65 in Ireland,45 Japan84 and Turkey85 and in ≥ 80 years in Japan86 and USA87.

National or multicenter registries are the most reliable to know the epidemiology of biopsied kidney diseases and allow comparisons; in Table 1, are indicated most of these studies, including those made in the UK,88–91 France,92,93 New Caledonia,94 Italy,95–101 India,102 United Arab Emirates,103 Japan,104–118 Denmark,119,129 Singapore,121 Peru,122 Australia,123 Korea,124 China,125 Czech Republic,126,127 Hungary,128 Croatia,129 Uruguay,130 Romania,131,132 Brazil,133–136 Lebanon,137 States States,138 Lithuania,139 Turkey,140 Colombia,141 Norway142–144 and Poland,145 among the most important. IgA Nephropathy is the most frequent nephropathy in Europe and Asia, while in the USA the FSG could be increasing.42,73,74,146

The REGN, which has more than 28,000 kidney biopsies in 2018, is only comparable to the registries of Italy34 and Japan118 that have collected, at least until their latest publications, between 15,000 and 26,000 biopsies, respectively.

In the present publication we want to summarize in broad terms the results of our REGN registry, think about the future, examine the current data in 2019, as well as the innovations necessary to maintain it updated and useful.

During the last 26 years (from 1994 to 2019), 27,116 kidney biopsies have been collected (92% first biopsy), with an average of 1042 biopsies per year. A total of 157 Nephrology Units have participated, the list is shown in the Appendix A.

The years of study have been grouped into 5 periods of 5 years each (except the last one that includes 6 years): 1994−1998, 1999−2003, 2004−2008, 2009−2013 and 2014−2019. The ages at the time of the biopsy they have been separated into 4 intervals: < 15 years, 15−65 years, 65−80 years and> 80 years. Histological diagnoses have been grouped into 5 sections: primary GN, secondary GN, tubulointerstitial nephropathy and vascular nephropathies. The rest (hereditary or difficult to classify) have been labeled as"other".

Table 2 indicates the number and percentage of biopsies performed in each time interval according to the age group.

The median ages and creatinine at the time of the renal biopsy of the entire population are 50 years and 1.6 mg / dl, respectively (neither one have a Gaussian distribution). Males predominate over females, with a ratio of 1.5. The prevalence of hypertension is 55%. In Table 3 these values are given for each age group.

Regarding the study method, 74.7% of the biopsies had a simultaneous study with an optical microscope and immunofluorescence, 17.8% also had electron microscopy, while 7% only had a study with optical microscopy and 0.5% only immunofluorescence.

The proportions of the renal syndromes at the time of the renal biopsy are indicated in Fig. 1.

Fig. 1.

Distribution of renal syndromes at the time of renal biopsy.

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Figs. 2 and 3 show the overall prevalence of all grouped kidney biopsies and for specific diagnoses, respectively.

Fig. 2.

Prevalence of nephropathies by groups.

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Fig. 3.

Prevalence of specific nephropathies biopsied.

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Figs. 4–7 summarize the prevalence in the different age ranges.

Fig. 4.

Prevalence of biopsied kidney disease in patients <15 years.

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Fig. 5.

Prevalence of biopsied kidney diseases in patients 15-65 years.

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Fig. 6.

Prevalence of biopsied kidney diseases in patients 65-80 years.

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Fig. 7.

Prevalence of biopsied kidney diseases in patients > 80 years.

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Figs. 8 and 9 show the trend of the most frequent kidney pathologies, grouped and by histological diagnoses, respectively.

Fig. 8.

Evolution of the most frequent biopsied pathologies by groups.

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Fig. 9.

Evolution of the most frequent specific pathologies.

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Figs. 10–13 show the trends of the biopsied pathologies in each age interval, <15 years, 15-65 years, 65-80 years and > 80 years, respectively.

Fig. 10.

Evolution of the most frequent biopsied pathologies in patients <15 years.

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Fig. 11.

Evolution of the most frequent biopsied pathologies in patients 15-65 years.

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Fig. 12.

Evolution of the most frequent biopsied pathologies in patients 65-80 years.

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Fig. 13.

Evolution of the most frequent biopsied pathologies in patients > 80 years.

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Tables 4 and 5 summarize the conclusions of all these results.

Nephrology has undergone numerous changes in recent years and kidney diseases that require biopsy have not been unaffected by these modifications. The emergence of new entities (C3 GN, among others) stands out, as well as a new approach for the classification and reporting GN.147,148 Therefore, the registries must adapt to these changes in order to collect the data in a uniform and modern manner. Without a doubt, the REGN needs some changes such as:

• a)

  Modification of the data completion sheet, with an extension of the clinical syndromes that indicate the reason to perform the renal biopsy (eg: nephrotic syndrome + acute renal failure; urinary alterations + hypertension).

• b)

  Possibility of selecting various pathologies detected in the renal biopsy (eg: IgA N + nephroangiosclerosis; diabetic nephropathy + extracapillary GN).

• c)

  Improve data collection to find out the incidence of the different pathologies “p.m.p”. according to the reference population of the center performing the kidney biopsies.

• d)

  Adapt the classification of kidney disease according to the new system proposed at the Mayo Clinic.147

• e)

  Increase participation, especially in Child Nephrology Centers.

• f)

  Promote multicenter studies and perform studies or clinical trials based on the data obtained.

• g)

  Maintain the analysis of the data and its subsequent publication, to determine changes in prevalence and incidence, as well as to evaluate correlations between clinical syndromes and the histological substrate.

• h)

  Incorporate information on associated morbidity, in order to establish the diagnosis of secondary forms (eg, viral or other infections, tumors, among others), given the availability of new biomarkers.78

Finally, the REGN must remain active to maintain the achievements, accumulated experience and number of biopsies. Since it is one of the largest and most reliable registries in the world, it must continue to provide data for the improvement of clinical practice and for the development of clinical research. Knowing the quality and quantity of participating centers - despite the absence of some of them - it is predictable that the activity will not decline in the coming years.