The significance of variation in the selectivity of proteinuria

The selectivity of proteinuria has been determined immunochemically at least 4 times over periods of 3 years or more in 27 children and adolescents who had been investigated by renal biopsy. Variations of the selectivity outside the limits of experimental error were observed in 14 patients, in 8 of whom there was a progressive decline. Six of these 8 had focal and segmental glomerular lesions, including one case of Alport's syndrome, and 2 had proliferative glomerulonephritis. Two different anomalies of relative IgG clearance were noted: in proliferative glomerulonephritis there was a constantly low clearance, and in focal glomerulosclerosis an elevated clearance increasing with time. Indirect evidence suggests that the latter may be due to the presence of low molecular weight IgG fragments in serum and urine.