Aspects on tubular proteinuria.

Tubular proteinuria, or low molecular weight (LMW) proteinuria, is less common than glomerular proteinuria, but is often of clinical significance. Both qualitative analysis of the urinary protein pattern by electrophoresis and quantitative estimations of various LMW-proteins are now usually available in the clinical routine laboratories. It is thus possible to look for LMW-proteinuria, as a sign of damage to the function of proximal renal tubules. For this purpose beta 2-microglobulin may be used as marker protein. Chronic cadmium poisoning and the Balkan nephropathy are examples of conditions which have been extensively studied by the use of LMW-protein determinations. In this context also some rare hereditary disorders deserve to be specially mentioned. Toxic injury to the kidneys, by drugs or other agents, often affect the kidney tubules early in the course and may be identified by LMW-protein analysis. Also in other clinical situations LMW-proteins in the urine may be used for investigative or research purposes.