• Freelite® FLC assays utilise sheep polyclonal antisera, and are validated for use with serum, urine and CSF.
  • FLC assays from other manufacturers are typically restricted to a different range of sample types.
  • Many other FLC assays utilise monoclonal antibodies, which may not recognise all FLC polymorphisms.
  • Freelite assays have been used as the “gold standard” reference calibrators for other FLC assays, although, in practice, values frequently show poor correlation.
  • Freelite is the only FLC assay recommended by name by the International Myeloma Working Group. Guidelines that are based on Freelite data cannot be applied to other FLC assays.

Clinical studies involving the use of free light chain (FLC) immunoassays have been published in scientific journals since the 1960s. A variety of assay formats have been described including radioimmunoassay, enzyme immunoassay (EIA), radial immunodiffusion, turbidimetry and nephelometry; and some have been claimed to be specific for the measurement of FLCs in serum [198]. However, it is only since Freelite FLC assays (Binding Site, UK) became commercially available that serum FLC (sFLC) measurement has come to be an integral part of routine clinical practice for the diagnosis and management of monoclonal gammopathies. Indeed, sFLC analysis is now included in various national and international guidelines (Chapter 25). In some countries, products intended for measurement of FLCs are commercially available from other manufacturers. This chapter provides an overview of the assays available, discusses the relative merits of polyclonal versus monoclonal antisera and presents data from the various published comparison studies.