Recommendations for the quantification of serum monoclonal components.

The quantification of MC provides a surrogate for monitoring the size of the population of malignant cells in patients affected by plasma cell disease (PCD). Consequently, clinical and laboratory guidelines on diagnosis, risk stratification and monitoring of PCD recommend MC quantification as a key information for patient management. To do that, liquid phase immunochemical determination of IgG, IgA and IgM in serum should not be used, because of the inability of the technique to distinguish between monoclonal and polyclonal immunoglobulins. However, new available immunoassays specifically measuring free light chains, or the "so-called" Hevylite assay, may reliably quantify specific MC. As a general recommendation, MC should be quantified on agarose gel electrophoresis by scanning densitometry or from capillary zone electrophoresis readout only, provided that a high resolution electrophoresis is performed and a low concentration MC obscured by other proteins is not present. For integration of the MC peak on electrophoresis, perpendicular drop method is recommended. MC is a critical "analyte" as the potential analytical pitfalls (detection limit depending on the position of the MC and on the polyclonal background, poor linearity of scanning methods, precision performance) show. Thus, a comprehensive program of IQC of MC quantification should be implemented as well as an EQAS.