: In a group of 400 nephrotic patients, both adults and children, the histological picture seen on renal biopsy, the selectivity of differential protein clearances, and the response to corticosteroid therapy where applied were studied. The only discernible difference was that of the relative incidence of underlying renal disease; in particular, the much greater incidence of “ minimal change ” lesions and the near absence of glomerular disease secondary to systemic disorders in children. Highly selective differential protein clearances were strongly associated with response to steroids within eight weeks, and this depended on the relation between this type of protein clearance and the minimal change lesion, which was the only histological appearance associated with complete response to corticosteroid therapy within eight weeks. Neither renal biopsy nor studies of proteinuria allowed prediction of which responding patients would subsequently relapse. Studies of differential protein clearances allow the paediatrician to avoid renal biopsy with safety in nephrotic children aged 1 to 5 years, but cannot distinguish any given renal disease with certainty. Generalized diseases affecting the kidney are usually associated with poorly selective differential protein clearances. Within all groups the most severe changes were usually associated with the least selective differential protein clearances, and vice versa. © 1968, British Medical Journal Publishing Group. All rights reserved.
