Comparison of serum immunofixation electrophoresis and free light chain assays in the detection of monoclonal gammopathies.

BACKGROUND: Diagnosis of monoclonal gammopathies (MGs) is determined by demonstration of a monoclonal immunoglobulin molecule or chain in serum and/or urine. Previous results on immunofixation electrophoresis (IFE) and quantitative free light chain (FLC) measurements have been conflicting.

PATIENTS AND METHODS: The purpose of this study was to compare IFE with serum FLC assays in the detection of MG. Between November 2006 and November 2007, results on routinely ordered serum IFE specimens were compared with independently conducted FLC assays.

RESULTS: Monoclonal gammopathies were identified in 144 specimens by IFE; 73 patients (50.7%) had a normal kappa/lambda ratio in the FLC assay. Also, 44.6% of samples with IgG and IgA M-proteins had a normal kappa/lambda ratio. Of 357 sera that showed no M-protein by IFE, 95.8% exhibited a normal kappa/lambda ratio. Out of 11 patients with light chain disease, 9 had abnormal kappa/lambda ratios. It is unclear why half of the patients with MG by IFE had normal kappa/lambda ratios. Lower M-components in these patients suggested that some had monoclonal gammopathy of undetermined significance.

CONCLUSION: For screening purposes, serum IFE should be carried out in patients with suspected MG.