Bence Jones proteinuria and myeloma kidney.

Bence-Jones proteinuria refers to urinary excretion of monoclonal light chains. It results from exclusive production of one light chain, or the unbalanced synthesis of heavy and light chains, with the latter being in excess. Free Kor A-light chains are therefore excreted alone or in addition to complete immunoglobulin molecules carrying the same light chain type. Free light chains are low molecular weight proteins that diffuse to the whole extracellular compartment. Within the kidney they are filtered through the glomeruli, reabsorbed in the proximal tubule by receptor-mediated endocytosis and degraded in the tubular cells by lysosomal enzymes. Light chains appear in the urine when the metabolizing capacity of the nephron is exceeded. They are not detected by dipstick analysis, but the conventional sulphosalicylic acid test is generally reliable for screening. Free light chains usually migrate with <x-2 mobility on electrophoretic techniques. Identification of the isotype (K or X) requires immunoelectrophoresis or immunofixation of the urine.