Poor performance of the total kappa/lambda light chain quantification in the diagnosis and follow-up of patients with multiple myeloma.
The gold standard for paraproteinemia screening in plasma cell disorders has been serum protein electro- phoresis (SPE) with immunofixation electrophoresis (IFx); serum total and free light chain quantifications have also been used. To define the role of SPE, IFx and serum total light chain (sLC) determinations in patients with multiple myeloma (MM), both at diagnosis and at maximum response during treatment follow-up. These serological studies were performed in a group of 62 patients with MM at diagnosis, and in a subset of 29 patients at the point of maximum response to treatment. At diagnosis, we found an abnormal SPE in 58%, an abnormal IFx in 92% and an abnormal sLC in 45% of the 62 patients; 64% had simultaneously abnormal results in all three serological studies. IFx alone proved to be the most sensitive of all three assays, followed by SPE, which was redundant in most instances with sLC and IFx. At maximum response, the abnormal SPE normalized in 7 cases, the abnormal IFx in 7 cases and the abnormal sLC in 7 cases. There were 12 instances in which an abnormal IFx was found despite normal sLC, and one case in which a normal IFx was found in the presence of abnormal sLC. The association between IFx and sLC was highly significant (r = 0.9274611, p < 0.000001), despite instances where a positive result for IFx was associated to a normal sLC. All three serological methods should ideally be simultaneously performed in patients with MM both at diagnosis and throughout therapy. In this series, the total sLC assay was not more sensitive than IFx neither at diagnosis nor during follow-up.