Incidence of biopsy-proven glomerulonephritis

Ole Wirta 1 2 3 Jukka Mustonen 1 2 3 Heikki Helin 0 2 Amos Pasternack 1 2 0 Department of Pathology, Helsinki University Hospital 1 Medical School, University of Tampere 2 The study was carried out from 1976 to 2000 in Western Finland. One university hospital (UH) and five central hospitals (CH1-5), all of them secondary referral centres , participated, for various lengths of time, the UH and one CH from 1976. The other CHs participated from 1980, 1982, 1990 and 1995, respectively. The common denominator for participating is that the kidney biopsy light microscopy (LM) specimens have been read by a single renal pathologist (H.H.) 3 Department of Medicine, Tampere University Hospital Background. The reported biopsy-proven glomerulonephritis incidence varies according to population characteristics, the unknown true glomerulonephritis incidence and biopsy rate. Reported glomerulonephritis incidence should be evaluated against the biopsy rate. Methods. We report here the glomerulonephritis incidence in our University Hospital (UH) consecutive biopsy material. It is compared to those from surrounding central hospitals (CH), previous singlecentre studies and European biopsy registries (EBR). Biopsy rate, when reported, has been considered. Results. The annual biopsy rate/105, median (min-max), at the UHs was 25.4 (15.6-35.1). At the CHs it was 8.7 (5.1-12.6). In previous single-centre studies it has been 18.7-21.5. In the EBRs it has been between 1.0 and 6.9 when reported. The annual incidences (median, min-max) per 105 (1980-2000) at the UH were as follows: proliferative glomerulonephritis (9.5, 6.8-18.1), non-proliferative glomerulonephritis (6.7, 3.4-12.6), the four major glomerulonephritis groups MesGN (7.7, 4.4-15.9), ECGN/FPGN-complex (1.4, 0.5-3.2), MCGP/ FSGS-complex (0.9, 0.2-2.7) and MGN (1.4, 0.52.4) these which findings were compatible with the single-centre studies and higher than those of the CHs and in the EBRs. Biopsy rate had a major impact on the annual glomerulonephritis incidences explaining 60% of the variation. The relative frequency of MesGN was the highest by all observers, followed by the ECGN/FPGN-complex, MGN and MCGP/ FSGS-complex whose frequencies did not differ much. For every patient commencing renal replacement therapy (Finnish Renal Replacement Registry Data) due to glomerulonephritis there were about 11 subjects with biopsy-proven glomerulonephritis, a relationship compatible with previous reports. Conclusions. The incidence of any glomerulonephritis of 17.6 per 105 population was comparable to those from the single-centre studies, but higher than in European biopsy registries, a fact largely explained by biopsy rates. Introduction The incidence of glomerulonephritis varies according to the population genetic and demographic characteristics, environmental factors like climatology, socioeconomics, prevalence of infectious diseases and time period [1,2]. In addition, the incidence varies according to the detection level of urinary findings, the biopsy resources of the community and the biopsy policy which are reflected as the biopsy rate. A universally valid epidemiology does not exist. One has to consider race, demography, population, era and biopsy rate. Kidney biopsy reports from single centres do exist, but reports considering biopsy rate are rare. In fact, few reports with control of the background population data, biopsy rate and biopsy policy over time exist. This is a report on the result from our university hospital compared to that of the Western region of Finland served by central hospitals (genetical and environmental equality), and especially to those studies concerned with European populations (socioeconomic equality) which have reported biopsy rate and biopsy indication. For details see Table 1. Subjects and methods Population Observations Biopsy rate per 105 Glomerulonephritis incidence per 105 Reference National Registry Denmark 19851997 5.2 106 National Registry Italy Torino Italy Moldova/Banat Romania Twenty-eight Czech centres Republic Brittany France National Registry Spain Victoria Australia 19871993 Virtually all Centres 19701994 2 106 19952004 6.2 106 19942000 19761990 391 265 19941999 Ninety-three centres 19951997 4.5 106 4.0 calculated 18.720.116.3 9.38.86.7 4.8 >3.5 The definition of glomerulonephritis varies between studies in terms of any-, primary-, secondary-. For details see appropriate reference. NG, not given. and all of the immunofluorescence (IF) specimens by J.M. or occasionally by H.H. The Western region of Finland is an area with a high standard of living, a population nearly totally of Caucasian race, an extensive primary health care system and low incidences of chronic infectious diseases like impetigo, hepatitis C and B, and HIV-related conditions. Nephropathia epidemica caused by Puumala hantavirus is endemic (seroprevalence 5%). It causes acute reversible renal failure with albuminuria and haematuria [3]. Routine urinary screening is carried out in maternity and child health welfare clinics, schools, work-places and some military service health systems (thus, nearly all young males are screened). The recruitment threshold for a kidney biopsy is low. Population data are electronically available from 1980 onwards. The incidences were calculated from 1980 to 2000 at the UH. The population in the area has been stable in terms of numbers, UH median 423 689, minmax 407 096 447 051 and CH15 median 812 275, minmax 790 177 822 376. All paediatric patients in the study area have been studied at the UH. Sixty-eight percent of the biopsies were carried out at the UH. For detailed biopsy rate data at the UH, see Figure 1. Kidney biopsy at the UH has been carried out in subjects with proteinuria with or without microhaematuria or renal failure or as part of the work-up of known or suspected systemic diseases. A bleeding diathesis, a single functioning kidney, small kidneys, multiple cysts, actual urinary tract infection and non-compliance have been excluded in the procedure. Other exclusions were a presentation suggesting diabetic nephropathy, evident myelomatosis, communityacquired acute renal failure caused by Puumala hantavirus after 1989 and isolated haematuria during the nineties. The same principles have largely been applied at the CHs but the actual decision to carry out a biopsy has been taken locally by an internist or nephrologist. The conduction of this report is retrospect and has not influenced any biopsy decision. Informed consent has been obtained in all subjects. Any applied statistical test is indicated in the text. The clinical data given in the report and the pathology (LM, IF) have initially been centrally stored at the Department of Pathology at the UH. They have been re-read and structurally classified by one of the authors (O.W.). The data contain information about the (i) centre, (ii) time of biopsy and (iii) the renal findings (haematuria, proteinuria, nephritic sy (...truncated)