Serum free light chain measurements for identifying and monitoring patients with nonsecretory multiple myeloma

Using sensitive, automated immunoassays, increased concentrations of either kappa or lambda free light chains (and abnormal kappa/lambda ratios) were detected in the sera of 19 of 28 patients with nonsecretory multiple myeloma. Four other patients had suppression of one or both light chains, and the remaining 5 sera had normal or raised free light-chain concentrations with substantially normal kappa/lambda ratios. Six of the patients with an elevated single free light chain, who were studied during follow-up, had changes in disease activity that were reflected by the changes in free light-chain concentrations. It is concluded that quantification of free light chains in serum should prove useful for the diagnosis and monitoring of many patients with nonsecretory myeloma.