Quantitative determination of urinary protein components of children with postural proteinuria.

Twenty-one protein components were measured in urine specimens from 12 subjects with postural proteinuria in the recumbent posture and after a period of upright lordotic posture. The lordotic posture produced an increased urinary excretion of total protein and 19 protein components, particularly of albumin, IgG globulin, and transferrin (128, 68, and 167-fold, respectively). However, 90 min after the lordotic posture, most of the protein components returned to initial values, whereas albumin, IgG globulin, and transferrin remained high. beta 2-Microglobulin, retinol binding protein, and lysozyme showed the smallest increases after the lordotic posture. These findings suggest that proteinuria occurring after the lordotic posture may be characterized by an increased glomerular permeability.