Measurement of free kappa and lambda chains in serum and the significance of their ratio in patients with multiple myeloma

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Abstract
Summary.: An inhibition enzyme‐linked immunoassay technique using commercially available antibodies has been developed for the quantitation of both kappa and lambda light chains in the serum of patients with B‐cell malignancies. Assay conditions were selected to enable measurement of free light chains in the concentration range between 0.1 and 20 mg/1. The normal range for free lambda chains in serum was found to be 0.4–4.2 mg/1 and for free kappa chains it was 1.6–15.2 mg/1. At diagnosis the serum of most patients with multiple myeloma contained increased levels of the malignant free light chain and in some cases there was also elevation of the non‐malignant light chain. The absolute level of the malignant light chain at diagnosis did not correlate with survival nor with laboratory parameters such as IgM or creatinine. A correlation with β2M and serum paraprotein levels was evident only in cases of IgA myeloma. Although the absolute level of free serum light chain had no value as a prognostic indicator, the ratio of kappa: lambda chains closely followed the clinical assessment of disease status, being near the normal range (1.2–9.1) in plateau phase or stable disease. During periods of progressive disease this ratio ranged from 19 to 460 (n=14) in patients with kappa myeloma, and 0.0013–0.14 (n= 9) in patients with lambda myeloma. Determination of the ratio of free light chains in the serum may allow effective monitoring and earlier warning of disease progression in patients with multiple myeloma.

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