The Free Light Chain (FLC) assay measures the levels of free kappa (κ) and lambda (λ) immunoglobulin light chains in the blood. Immunoglobulins (antibodies) are made of heavy and light chains, and light chains are normally present in small amounts in circulation. An imbalance or abnormal increase in free light chains can indicate plasma cell disorders such as multiple myeloma, light chain amyloidosis, or other monoclonal gammopathies.