Current concepts in proteinuria.

Proteinuria, long recognized as a sign of renal disease, is a common laboratory abnormality in children and adults. Proteinuria may be transient or persistent; when persistent, the cause must be determined. Proteinuria may be primarily glomerular or tubular in origin. Glomerular proteinuria is usually an important concern. Tubular proteinuria often indicates the presence of tubulointerstitial or obstructive renal disease. Screening tests are available to detect albumin (the major protein in glomerular proteinuria), but there are no simple tests for immunoglobulin light chains and low-molecular-mass proteins, which predominate in overflow proteinuria and tubular proteinuria. These small proteins can only be detected by more sophisticated assays such as electrophoresis, isoelectric focusing, and chromatography. The association of glomerular and tubular types of proteinuria with specific disorders is reviewed in this paper, and current concepts in laboratory methodology for the study of proteinuria are summarized.