Immunochemical Quantification of Free Light Chains in Urine

Abstract

Quantitative measurements of plasma and urinary paraprotein concentrations play a major role in the monitoring of patients with multiple myeloma. The concentrations are routinely estimated from the size of the M-spike on protein electrophoresis (PEL) or by automated immunologic assays for IgG, IgA, IgM, IgE, or IgD. In the case of light chain myeloma and intact immunoglobulin myeloma with predominant light chain production, light chain concentrations could, until recently, be measured only by the size of the urinary light chain M-spike on PEL or by the measurement of the total (free and bound) light chain concentrations. A latex-enhanced assay (Freelite; The Binding Site, Ltd.) measuring free light chains (FLCs) in serum and urine has recently become available for the BNII (Dade Behring) analyzer. The Myeloma Management Guidelines (1) recommend the Freelite test for serial monitoring of the FLCs in serum, but periodic 24-h urine collection is still required for Bence Jones proteinuria (BJP) and total urinary protein (TUP) quantification. Depending on the glomerular and tubular function, serum and urine FLC concentrations may not change to the same degree (2), so that monitoring of serum FLC alone is questionable for revealing the actual degree of disease in patients with BJP and tubular dysfunction. We evaluated the analytical performance of the immunochemical test for serum and urine with the BNII analyzer. The test uses antibodies that specifically recognize an epitope …