The value of IgG-uria in predicting renal failure in idiopathic glomerular diseases. A long-term follow-up study

Background. Proteinuria is the hallmark of glomerular disease and non-selective proteinuria is often associated with progression to renal failure. The predictive value of urine IgG excretion was studied comprehensively in patients with nephrotic syndrome. In the present follow-up study, we examine the predictive value of IgG-uria in patients with idiopathic glomerular diseases with a wide range of proteinuia. Methods. A total of 189 (113 males and 76 females) patients with idiopathic glomerulonephritis and serum creatinine of less than 150 μmol/L diagnosed between 1993 and 2004 were followed up to their last visit in 2009. Measurement of urine excretion of albumin, IgG, and protein HC were performed in the early morning of spot urine samples collected at the time of the diagnostic renal biopsy. Patients were stratified according to urine protein concentrations and the progression rate to end-stage renal disease (ESRD) calculated using Kaplan-Meier survival analysis. ESRD was defined as the start of renal replacement therapy. Results. During the study follow-up time of 1429 person-years; 26 (13.8%) patients reached ESRD. The overall mean kidney survival time of studied patients with serum creatinine less than 150 were 13.4 years. The incidence rate of ESRD was ∼18 per 1000 person-years. Stratified analysis identified urinary excretion of IgG, but not albuminuria, as predictor of ESRD. The progression rate to ESRD was 36 per 1000 person-years in patients with urine IgG concentration exceeding 5 mg/mmol urine creatinine, compared to a progression rate of 6/1000 person-years for patients with lower levels of urine IgG. Conclusion. The findings of the study suggest that at early stages, the level of IgG-uria is useful to be used in risk stratification of patients with proteinuric glomerular diseases.