Tubular function in multiple myeloma.

In 42 myeloma patients our results confirm the association of light chain proteinuria and renal damage, but suggest that while the amount of light chain excreted is an important factor, only some light chains are nephrotoxic. The excretion of the proximal tubular cell lysosomal enzyme N acetyl B D glucosaminidase was a sensitive index of tubular injury, while the presence of low molecular weight proteinuria (Retinol Binding Protein and Lysozyme) was shown to indicate tubular dysfunction in a kidney sufficiently damaged to produce an impaired GFR. Isolated defects of distal tubular function (acid load response and concentrating ability) were rare. Such changes were seen mainly as part of global renal impairment and were usually associated with such specific pathophysiological conditions as plasma hyperviscosity or tubular crystal deposition. Hypercalcemia had a specific effect on the concentrating ability independent of any impairment of renal acidification.