Complementarily of urine analysis and serum free light chain assay for assessing response treatment response: Illustrated by three case examples

► Treatments decrease monoclonal proteins in patients with plasma cell dyscrasia and improve survival. ► Low concentration monoclonal free light chains (FLC) are difficult to detect by the serum FLC assay. ► Urinary immunofixation electrophoresis on concentrated specimens is often more sensitive and specific. ► These results support the proposal that urinary assay is useful with serum FLC concentrations < 100 mg/l.