OBJECTIVETo investigate the clinical significance of serum free light chain (sFLC) detection in light chain multiple myeloma (LCMM).

METHODSA total of 37 newly diagnosed LCMM patients were enrolled in this study, including 17 patients with k light chain type and 20 patients with λ light chain type, the sFLC and 24 hours urine light chain (ULC) were measured before and after chemotherapy. The correlation of sFLC level with ULC and renal impairment was analyzed.

RESULTSAll the patients displayed an abnormally increased level of sFLC at diagnosis wtih median value of 105.44 mg/L and 146.39 mg/L for k and λ light chain types, respectively. The sFLC did not correlate with ULC before and after chemotherapy. Among the 12 patients with very good partial remission and normal ULC level, the sFLC still was abnormally increased in 8 patients. Renal impairment was associated with the urine λ-type light chain, and the area under the ROC curve of urine λ light chain at diagnosis is 0.792 (P = 0.031).

CONCLUSIONAll patients with LCMM show an abnormally increased level of sFLC at diagnosis. sFLC can be used to monitor the response to chemotherapy because it is more sensitive for analysis of therapeutic effect than urine λ light chain.