Discrimination of Monoclonal Gammopathy Using Immunoassay for Free Light Chains

Park, Il Joong; Cho, Sung Ran; Lee, Wee Gyo

Abstract

BACKGROUND
Immunoglobulins exist in the serum, mostly in a union type of heavy and light chains. Free light chain types exist in an extremely small quantity and are useful in the diagnosis and follow up of multiple myeloma, but are also increased in autoimmune diseases such as SLE. The aim of this study was to evaluate the usefulness of the serum free light chain in discriminating between monoclonal and polyclonal gammopathy. METHODS: Between January and June of 2003, we identified 15 patients with monoclonal gammopathy and 12 patients with polyclonal gammopathy on serum protein electrophoresis (SPEP) and immunofixation electrophoresis (IFE). We measured the serum concentration of the free light chain using Beckman Coulter IMMAGE(TM) analyzer with FREELITE(TM) reagents and calculated the kappa/lambda (kappa/lambda) ratio. We also measured the free light chain of 35 healthy controls to establish a reference range. RESULTS: The reference ranges established in this study were 4.97-12.84 mg/L for kappa light chains, 6.71-18.09 mg/L for lambda light chains, and 0.46-1.01 for the kappa/lambda ratio. The free light chains were abnormal in all 27 but 2 patients with polyclonal gammopathy on SPEP. The kappa/lambda ratio was abnormal in 12 of the 15 patients with monoclonal gammopathy and in none of the 12 patients with polyclonal gammopathy. CONCLUSIONS: Our results suggest that the kappa/lambda ratio can be a useful tool to discriminate between monoclonal and polyclonal gammopathy, especially in the case of vague SPEP results, or when monoclonal gammopathy is suspected in SPEP.