Serum free light chain (FLC) assay is an important advance in the diagnosis and monitoring of monoclonal light chain diseases, Multiple Myeloma and a complementary test to serum protein electrophoresis and immunofixation.

Use of the assay has grown globally since that time and other retrospective clinical studies have shown the clinical utility of FLC in serum as a complementary test to serum protein electrophoresis (SPEP) for the diagnosis and monitoring of monoclonal light chain diseases.

Monoclonal immunoglobulin free light chains are important tumour markers often present in serum and urine of patients with monoclonal gammopathies. Serum kappa (κ) and lambda (λ) FLC assays measure total polyclonal and monoclonal FLC in serum and the calculated κ/λ FLC ratio is a surrogate measure of clonality.