Replacing urine protein electrophoresis with serum free light chain analysis as a first-line test for detecting plasma cell disorders offers increased diagnostic accuracy and potential health benefit to patients.

OBJECTIVES To determine the most clinically effective diagnostic testing strategy for plasma cell disorders in the clinical laboratory. METHODS Serum and urine samples from 2,799 patients with suspected plasma cell dyscrasias were tested by alternative diagnostic testing strategies consisting of serum protein electrophoresis (SPE) with either urine protein electrophoresis (UPE) or serum free light chain (sFLC) analysis. RESULTS The combination of sFLC analysis and SPE had the greatest sensitivity (100%), detecting abnormalities in all 124 patients diagnosed with plasma cell disorders. Routine sFLC testing would have had much potential health benefit for two patients in the study population. First, a patient who had a markedly abnormal sFLC result was diagnosed with light chain deposition disease by renal biopsy, but no abnormality was detected by SPE or UPE. Second, a patient diagnosed with multiple plasmacytomas following biopsy of a lung tumor had a grossly abnormal sFLC result but an equivocal weak-positive SPE result, and no urine sample was received by the laboratory for the patient. CONCLUSIONS Our study suggests that the combination of SPE and sFLC analysis is the most clinically effective first-line diagnostic testing strategy for detecting plasma cell disorders in the clinical laboratory.