[Clinical significance of measurement of free light chains]

Plasma cells usually produce free light chains (FLCs) together with intact immunoglobulins, irrespective of the presence of monoclonality. To easily determine the concentration of FLCs in both serum and urine, a new kit using a latex-enhanced immunoassay (Freelite, Binding Site, UK) has recently become available. According to original data of Binding Site, this kit can precisely show an increase in lambda- and kappa-FLCs in serum as well as abnormal kappa/lambda ratios with high-level sensitivity and specificity for multiple myeloma, including intact immunoglobulin and non-secretory types. Serum FLCs well reflect the disease activity of multiple myeloma, and apparently decrease after chemotherapy. We investigated serum FLCs using this kit in another monoclonal plasma cell disorder, primary systemic AL amyloidosis. Almost all patients showed increases in either lambda- or kappa-FLCs as well as abnormal kappa/lambda ratios, as seen in multiple myeloma. Their prognosis was very poor when the kappa/lambda ratio remained abnormal even after intensive chemotherapy. Serum FLCs may be a useful marker on making a diagnosis, but also in evaluating the clinical efficacy of chemotherapy in monoclonal plasma cell disorders, such as multiple myeloma and primary systemic AL amyloidosis.