Establishment of Serum Reference Range for Free Light Chains and its Clinical Usefulness in Multiple Myeloma

Kang, So Young; Suh, Jin Tae; Lee, Hee Joo; Yoon, Hwi Joong; Lee, Woo In

Abstract

BACKGROUND
M protein, as a marker for monoclonal gammopathy, has been evaluated by protein electrophoresis (PEP) and immunofixation electrophoresis (IFE). Recently a highly sensitive, automated immunonephelometric assay for measurement of free light chains (FLCs) in serum and urine has been developed for the identification and monitoring of patients with monoclonal gammopathy. METHODS: We measured the concentration of kappa and lambda FLCs in 120 healthy individuals aged 20 to 80 years to establish the reference range of kappa and lambda FLCs and kappa/lambda FLC ratio and in 61 serum and 14 urine samples from patients with multiple myeloma (MM) to examine the correlation between the amount of M protein indirectly calculated on PEP and the direct measurement of FLCs. RESULTS: The concentrations of kappa and lambda FLCs and the kappa/lambda FLC ratio in healthy individuals were not significantly related to age or sex. The 95 percentile reference ranges for kappa FLC, lambda FLC, and kappa/lambda FLC ratio were 8.5-23.7 mg/L, 9.5-23.5 mg/L, and 0.67-1.38, respectively. On the PEP performed with MM specimens, 18 cases did not show the evidence of M protein. But, they revealed abnormal FLC concentrations on FLC assay and a significant correlation was found between the amount of M protein and the concentration of kappa and lambda FLC. However, inconsistent results such as the concentra-tion of kappa+lambda FLCs being more than the total protein in urine or M protein in serum were found in 5 of the 14 urine and 1 of the 61 serum samples of MM patients. CONCLUSIONS: FLC assay showed a good correlation with PEP and was more sensitive and accurate than PEP. Therefore, FLC assay is useful for diagnosing and monitoring monoclonal gammopathy at an early stage of the disease and during a remission state after chemotherapy or peripheral blood stem cell transplantation.