Method for measuring the concentration of urinary proteins according to their molecular size category

We combined the use of a concentrating device (Minicon) and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate to semi-quantitate the concentration of (a) the collective low-molecular-weight proteins and (b) of albumin excreted in the urine of patients after renal transplantation. Analytical recovery of many serum proteins from samples concentrated 100-fold in the Minicon apparatus was about 70%. It was possible to examine many urine samples by polyacrylamide gel electrophoresis after concentration with this device. The reproducibility (CV) of the technique was on the order of 20% when albumin and low-molecular-weight protein were in about equal concentration. The method was adequate to differntiate glomerular and tubular proteinuria, because in glomerular proteinuria the ratio of albumin to low-molecular-weight proteins is about 20/1, whereas in tubular proteinuria the ratio is about 1/1.