The product of duration and amount of proteinuria (proteinuria index) is a possible marker for glomerular and tubulointerstitial damage in IgA nephropathy

Background/Aims: IgA nephropathy (IgAN) is one of the major causes for chronic renal failure (CRF). Presence of massive proteinuria, hypertension, increased serum creatinine level and sclerotic histopathological changes of the glomerulus are known to be determinants for the progression of CRF. However, the relationships between duration of proteinuria/hematuria and histopathological changes, which may be correlated with the renal prognosis, have not been clarified. Methods: A cross-sectional, univariate analysis of clinical parameters on the four glomerular and three tubulointerstitial histopathological grades in 57 untreated biopsy-proven IgAN patients (M/F = 32/25) was performed. Results: The age at the time of renal biopsy (35.2 ± 13.0 years; mean ± SD), average duration of proteinuria (5.3 ± 5.8 years), mean urinary protein excretion (0.99 ± 1.22 g/day), serum creatinine (Cr 0.97 ± 0.28 mg/dl), Cr clearance (Ccr 75.5 ± 29.4 ml/min), and blood urea nitrogen (BUN 15.4 ± 3.9 mg/dl) were well correlated with both histopathological grades. The product of duration (years) and urinary protein excretion (g/day) at the time of renal biopsy was more significantly correlated with glomerular and tubulointerstitial histopathological grades and serum Cr. Conclusion: The natural course of IgAN is steadily progressive depending on the duration and amount of proteinuria. The product of these two factors (proteinuria index) may be a useful predictor for glomerular and interstitial histopathological changes and the fate of renal function in IgAN.