Glomerular proteinuria as an early sign of renal-transplant rejection.

The introduction of cyclosporin gave rise to an additional problem in the surveillance of renal transplant patients, namely the differentiation between cyclosporin toxicity and acute transplant rejection. The development of assays for specific proteins in urine has produced a non-invasive solution to this problem. In 55 renal transplant patients the following proteins were determined daily in 24 h-urine samples: IgG, transferrin (TF), albumin, beta 2-microglobulin (beta 2-MG), retinol binding protein (RBP), alpha 1-microglobulin (alpha 1-MG) and alpha 1-antitrypsin (alpha 1-AT). All proteins were determined quantitatively using immunoluminometric assays and 10 microliters urine in dilutions from 1:1-1:100. The urinary protein excretion was related to the actual creatinine clearance as this index gave the best differentiation between normal and abnormal status. In 24 h-urine, intraindividual peaks of IgG, TF and albumin were seen regularly in acute rejection episodes. However, a peak in the "tubular" proteins (RBP, beta 2-MG, alpha 1-MG) could not be detected. After effective treatment of the rejection episode, the renal function improved and the protein excretion returned to prerejection episode levels. In bacterial infection of the urogenital tract, urinary alpha1-AT levels rose. They returned to normal after successful antibiotic treatment. In two cases of cyclosporin toxicity neither glomerular nor tubular proteins were excreted in abnormal amounts when compared with transplant patients without complications, the only changes being an increase in serum creatinine as a result of reduced renal function.