[Detection of serum free light chain and its clinical significance in nonsecretory multiple myeloma].

Objective: To explore the clinical significance of serum free light chain (sFLC) levels in nonsecretory multiple myeloma (NSMM).

Methods: Nine NSMM patients were hospitalized in our department from Feb 2002 to Sep 2006 and no M-components was found in their serum and urine by immunofixation electrophoresis (IFE). sFLC was assayed by immuno-nephelometry. The clonality of sFLC was estimated by serum kappa:lambda sFLC ratio. Meanwhile, serum immunoglobulin, total kappa and lambda light chain level were also determined in these patients.

Results: Increased serum concentrations of either kappa or lambda sFLC (and abnormal kappa/lambda ratios) were detected in 6 of 9 patients with NSMM although their serum immunoglobulin levels were not elevated and total kappa:lambda light chain ratios (1.32 - 2.20) were in the reference range. All the 9 patients had clonal IgH gene rearrangements.

Conclusion: Quantification of sFLC by immuno-nephelometry is more sensitive than that of serum total light chain measurement and is helpful in estimating the clonality of the light chain in patients with NSMM.