Laboratory testing in the evaluation of a monoclonal protein: A practical framework for interpretation

Monoclonal proteins are immunoglobulins secreted by identical but abnormal plasma cells that are clones of a parent cell. While routine screening in the absence of signs or symptoms of disease is not recommended, testing is indicated in the diagnostic work-up for multiple myeloma and other plasma cell disorders. When indicated, a serum protein electrophoresis with immunofixation and serum free light-chain assay should be performed to determine the type and quantity of monoclonal protein. Using a case-based approach, we highlight common misconceptions with monoclonal protein investigations, and suggest a practical framework for diagnostic interpretation.