Serum free light-chain assays have been used in a number of published studies which have indicated superiority over the urine tests, particularly for patients producing low levels of monoclonal free light chains, as seen in nonsecretory multiple myeloma[REF][REF][REF] and AL amyloidosis [REF].
A series of studies, principally from the Mayo Clinic, have indicated that patients with an abnormal free kappa / free lambda ratio have an increased risk of progression to active myeloma from precursor conditions including Monoclonal gammopathy of undetermined significance (MGUS),[REF][REF] Smoldering myeloma[REF] and solitary plasmacytoma of the bone [REF].