Freelite® sFLC assays are quantitative, latex-enhanced immunoassays that are performed on routine nephelometric or turbidimetric instruments (Chapters 5 and 37). Of all the methods used to detect monoclonal immunoglobulins, sFLC analysis has the highest analytical sensitivity for identifying monoclonal sFLCs (Table 4.1) .
The high clinical sensitivity of sFLC assays is dependent upon assessing the individual sFLC concentrations and the κ/λ sFLC ratio. Tumour suppression of the normal plasma cells in the bone marrow reduces the concentration of polyclonal uninvolved sFLCs, and thereby enhances the sensitivity of the κ/λ ratio.
Katzmann et al.  concluded that a combination of sFLC and SPE provided a simple and efficient initial diagnostic screen for the high-tumour-burden monoclonal gammopathies such as MM, Waldenström’s macroglobulinaemia (WM) and smouldering MM (SMM) (Chapter 23). International guidelines recommend that sFLC analysis in combination with SPE and sIFE is sufficient to screen for all pathological monoclonal plasmaproliferative disorders other than AL amyloidosis, which requires IFE of a 24-hour urine sample in addition to the serum tests (Chapter 25).