This study was designed to evaluate the occurrence and the type of proteinuria in 82 children with vesico-ureteric reflux (VUR) with or without renal scars. The urinary excretion of the high molecular weight protein albumin was taken as an index of glomerular alterations and the excretion of retinol-binding protein (RBP), beta(2)-microglobulin and brush border antigens (BBA) (measured by monoclonal antibody-based enzyme-linked immunosorbent assay) was taken as an index of tubular alterations. All such markers were increased in children with VUR and were related to the degree of renal function. Patients showing reduced creatinine clearance had very high levels of albuminuria, microproteinuria and BBA, with all these variables reciprocally correlated. In children with normal renal function however, only microproteins (not albumin or BBA) were slightly increased, thus indicating an isolated tubular defect without involvement of the proximal segment of the tubule. However, microprotein excretion did not correlate with the grade of scarring (99mtechnetium-dimercaptosuccinic acid scan), both RBP and beta(2)-microglobulin excretion being normal in 75% of children with radioisotopic signs of renal lesions but increased in 17% of children without scars. Therefore, tubular proteinuria identifies different groups of children with VUR but is not related to renal scarring. Prospective studies will define the usefulness of proteinuria as a reliable indicator of renal outcome.
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