Urine excretion of protein HC in proteinuric glomerular diseases correlates to urine IgG but not to albuminuria

Background. Proteinuric glomerular diseases often are associated with tubul ointerstitial injury, which imposes on the progression of renal failure. Tu bular damage is partly referable to toxic effects on the tubular epithelial cells induced by filtered plasma proteins. Patients with nonselective prot einuria, that is, increased urine excretion of high-molecular-weight plasma proteins such as IgG in comparison to albumin, often have poor renal outco me. The present observational study examined correlations between the degre e of tubular damage, measured by urine concentration of protein HC, and the levels of urine IgG and albuminuria. Methods. Measurements of urine concentrations of IgG, albumin, and protein HC were performed in 56 proteinuric patients (33 males and 23 females) with nondiabetic glomerular diseases at the time of the diagnostic renal biopsy and at a mean of 49 follow-up months. Results. A highly significant correlation between the urine IgG excretion a nd the urine protein HC concentration was found both at the start and at th e end of the observational time (r = 0.74 and 0.65, respectively, P < 0.001 ). Furthermore, alterations in the urinary excretion of the two proteins in single patients correlated significantly to each other (r = 0.84, P < 0.00 1). The correlation between the degree of albuminuria and the protein HC ex cretion was significant at the time of kidney biopsy, but ceased to exist d uring the follow-up time. Stepwise linear regression analysis showed that i n comparison with the creatinine clearance and albuminuria, only the change s in urinary IgG excretion were related to the corresponding changes in uri nary protein HC excretion (r = 0.84 and r' = 0.7, P < 0.001). Conclusion. The findings of the study suggest that the urinary protein HC c oncentration correlates to the degree of IgG-uria but not to the degree of albuminuria during the course of proteinuric glomerular disease. Whether th is correlation is to be explained by an intrinsic toxic effect on tubular c ells executed by IgG or perhaps by some other high molecular weight protein s, needs to be investigated further. However, the results contribute to the understanding of the poor renal survival in patients with glomerular disea ses and nonselective proteinuria.