Abstract
The selectivity of proteinuria has been determined from the relative clearances of α1-acid glycoprotein, albumin, transferrin and IgG in 190 children and adolescents. The precision of the determination of selectivity (C.V. = 3%) is greater than that of the individual protein clearances determined by a double immunodiffusion method (C.V. = 13–22%). Neither sample storage for a limited period nor concentrating the urine affects the selectivity value significantly; serial determinations in one patient for 24 h showed no diurnal variation.
The effectiveness of selectivity in predicting the steroid response in the nephrotic syndrome was found to be slightly superior when determined from all four proteins than from transferrin and IgG alone. Inclusion of α2-macroglobulin relative clearance in the selectivity determination often significantly alters the value determined from the other four proteins alone. The reasons for this are discussed. Demonstration of α2M in urine which has not been concentrated, strongly suggests the presence of a structural glomerular lesion.