Profile of renal permselectivity by simultaneous enzyme-linked immunosorbent assay of albumin, transferrin, IgG, and alpha 1-microglobulin with a new microplate reader.

A competitive enzyme-linked immunosorbent assay (ELISA) is described for determining a renal permselectivity profile involving the urinary proteins albumin, transferrin, IgG, and alpha 1-microglobulin (alpha 1-m). The ELISA reader uses a computer-controlled array of multiplexed light-emitting diode (LED)-photodiode pairs for rapid measurements of absorbance on microplates. A 3,3'-dimethylnaphthidine reagent adapts the 3,5,3',5'-tetramethylbenzidine chromophore to monochromatic LED emission at 550 nm. We applied this ELISA to the determination of renal permselectivity in healthy children and young adults and in children with insulin-dependent diabetes mellitus. The geometric means (and SD) of protein excretion rates in a group of 85 normal subjects were as follows: albumin, 3.5 micrograms/min (1.83); transferrin, 173 ng/min (2.76); IgG, 1.11 micrograms/min (2.22), and alpha 1-m, 0.98 microgram/min (2.36).