Discrepancy between FLC assays: Only a problem of quantification?

Immunoglobulin light chains not associated with heavy chains (free light chains, FLC) are found in serum. A growing clinical importance has been assigned to the quantification of the kappa and lambda FLC in serum in the management of plasma cell dyscrasias. At present, automated immunoassays are the only available techniques allowing quantitative determination of serum FLC. Unfortunately, the two reagents available for FLC assay, provide sometimes divergent results. It has been proposed that the different results, unpredictably affecting individual serum samples, are due the different reactivity of reagents against FLC oligomers that are known to be present to a variable extent in serum, especially when lambda FLC are involved. We report a case where we demonstrated that the two reagents recognized differently FLC monomer and dimers.