This test is a latex-enhanced, immunoassay that provides ultrasensitive detection and quantitation of free light chains (FLCs) in serum or urine earlier than electrophoresis. It is an aid in the diagnosis and treatment of multiple myeloma, lymphocytic neoplasms, Waldenstroms macroglobulinemia, and connective tissue diseases, such as systemic lupus erythematosus.
Approximately 15% of all cases of multiple myeloma produce only free kappa or lambda light chains in excess. These patients frequently show no abnormality on serum protein electrophoresis. Quite often urine is tested for the presence of these light chains, which are also called Bence Jones Proteins. However, the FLCs entering the urine are strongly influenced by renal tubular function. When clonal proliferation of plasma cells starts to develop, the FLC concentration increases in serum. Since
these small particles are rapidly cleared by the renal tubules, urine tests for FLCs remain negative until the tumor mass expands, and the FLCs in serum exceed the resorptive capacity of the renal tubules. Therefore, the measurement of FLCs in serum is an alternative to less sensitive urine testing. Changing concentrations of FLCs in serum relate better to changing tumor load than to concentrations in urine.