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Steroid-responsive idiopathic nephrotic syndrome (SRlNS) with minimal change disease (MCD) is the most common cause of nephrosis in childhood. MCD is no longer considered to be easily curable and the finding of minimal changes is no guarantee that the disease will not progress to renal failure or to another form of glomerulonephritis. In the present work, renal function was studied in subjects presenting with SRINS and MCD in childhood. Attention focused on glomerular filtration, integrity of the filtration membrane, reabsorption in the proximal tubule, and renal vessels. The influence of age, age at onset, recurrences, duration of the active phase, duration of remission, 24-hour protein loss and Up/UCr ratio on renal function was analyzed. An attempt was made to establish if patients with lasting remission require periodic follow-up by a nephrologist. The study group consisted of 31 subjects with SRINS in childhood. Remission of at least one year was ascertained at the time of study. A hyperfiltration subgroup (n = 11) with creatinine clearance (Ccr) of > 150 mL/min/1.73 m2 was formed. The control group included twelve healthy volunteers matched for age and gender. Creatinine and lithium clearance, fractional lithium secretion, and the Up/UCr ratio were calculated according to standard formulas. Albumin and immunoglobulin G secretion was measured using cross-star immunofixation. Protein content in urine was determined with the method of Exton and renal vessels were imaged using Doppler USG. Significant reduction in creatinine and lithium clearance was disclosed in SRlNS patients. The reduction was proportional to the time since the last episode of the disease. Glomerular hyperfiltration was found in 35.5% of subjects. Fractional lithium secretion was higher in the study than control group. This discrepancy was particularly evident in subjects with Ccr below 120 mL/min/1.73 m2. In 40% of subjects, mild selective proteinuria was confirmed which did not correlate with renal function. Renal vessels were free of thrombo-embolic lesions. Conclusions: l. Deterioration of renal filtration proportional to the time since the last episode of nephrosis was diagnosed in subjects treated for SRINS in childhood. Hyperfiltration revealed in 1/3 of subjects may be associated with a poorer prognosis. 2. Abnormal tubular reabsorption was observed solely in subjects with Ccr below 120 mL/min/1.73 m2. 3. Mild selective proteinuria was without any effect on renal function. 4. MCD had no long-term effect on renal vessels. 5. In spite of long lasting remission of SRINS with MCD in childhood, the risk of disease progression remains and follow-up is necessary. 

K e y w o r d s : minimal change disease – creatinine clearance – hyperfiltration – proteinuria – proximal reabsorption. 

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