kappa/lambda index for confirming urinary free light chain in amyloidosis AL and other plasma cell dyscrasias.

Primary systemic amyloidosis (AL), a disease involving the deposition of immunoglobulin light chains in tissue, is caused by a plasma cell dyscrasia. In the case of amyloidosis reported here, no monoclonal component was seen upon routine protein electrophoresis of serum or urine nor was a bone marrow analysis positive for AL. Immunofixation electrophoresis did not show a typical paraprotein band but did show, in the gamma region, two large diffuse bands and a lower concentration of oligoclonal-type bands, all of which stained for free lambda but not for free kappa chain. The ratio of kappa to lambda chains in urine was 0.178, much less than the ratio in serum (1.3). Six other urine samples from a group of patients with documented Bence Jones proteinuria also exhibited kappa/lambda ratios that differed manyfold from the ratios in their corresponding serum samples. On the other hand, the kappa/lambda ratios from seven controls (seven patients with generalized proteinuria unrelated to plasma cell dyscrasia) were similar in serum and urine. This difference between the kappa/lambda ratios from serum and urine can be expressed as a kappa/lambda index. The index was significantly different (P less than 0.01) between the two patient groups compared here, and was useful in confirming the presence of Bence Jones protein in this case with a difficult-to-interpret electrophoretic pattern. Although the kappa/lambda ratio has been widely used for confirmation and identification of monoclonal components in serum, its use in clinical laboratories has not been widely extended to urine. Comparison of serum and urine kappa/lambda ratios as a kappa/lambda index may help reduce the need for more complex immunoelectrophoresis techniques in identifying free light chains in urine.