Serum free light chain analysis for diagnosis, monitoring, and prognosis of monoclonal gammopathies

Measurement of free kappa and free lambda light chains plays a key role in diagnosis, monitoring, and prognosis for many patients with a monoclonal gammopathy. These assays are advocated by the International Myeloma Working Group (IMWG) as an essential component of the primary screening algorithm for suspected monoclonal plasma cell disorders.¹⁸ Markedly increased baseline clonal free light chain concentrations are associated with poor prognosis in amyloid light chain (AL) amyloidosis, multiple myeloma, and virtually every plasma cell disorder.¹⁸ An abnormal serum free light chain ratio at baseline is predictive of an increased risk of progression in patients with monoclonal gammopathy of undetermined significance.²⁰ Serial monitoring with serum free light chain analysis is recommended by the IMWG for patients with oligosecretory myeloma and AL amyloidosis. Additional data is needed to critically assess the utility of serum free light chain analysis as a serial monitoring technique in patients with multiple myeloma. The significance of isolated serum free light chain ratio abnormalities ("free light chain monoclonal gammopathy of undetermined significance") also needs to be explored.