Development of renal failure in IgA nephropathy: the importance of interstitial infiltration and deposition of fibrinogen.

We analyzed renal biopsy specimens of 60 patients with IgA nephropathy, 34 male and 26 female, aged 32, 8 +/- 9, 1. Patients were divided into 5 classes according to the morphological classification proposed on the basis of WHO criteria: 1, minimal lesions; 2, minor changes; 3, focal and segmental glomerulonephritis; 4, diffuse mesangial proliferation; and 5, sclerotic changes. Interstitial infiltration on optical microscopy and fibrinogen deposition on immunofluorescent microscopy were graded using a semiquantitative score. Clinical features (hypertension, proteinuria, erythruria/hematuria, renal function) were taken into consideration. The Mann-Whitney test was used for comparison of results between different classes. Classes 1 and 2 were younger (p < 0.01) and had significantly better renal function than classes 3 and 4. Proteinuria was significantly higher in classes 2 and 3 (p < 0.001) than the others. Macroscopic hematuria was more frequent in classes 1 and 2. Hypertension was absent in class 1 and correlated with the severity of histologic changes. Interstitial infiltration was absent in class 1 and also correlated with the degree of histological changes, but in contrast, fibrinogen deposits were more severe in earlier histological classes.