Serum Free Light Chain Measurement Can Replace Urine Electrophoresis in the Detection of B Cell Proliferative Disorders.

Retrospective studies have established the high sensitivity of quantitative serum free light chain (SFLC) measurement in the detection of patients with light chain myeloma, nonsecretory myeloma and primary amyloidosis. These disorders account for 15–20% of new diagnoses of B cell proliferative disorders and cannot be confidently excluded by current protocols without electrophoresis of both serum and urine. This prospective study evaluated whether the addition of SFLC to our first line investigations for B cell proliferative disorders detected additional patients with monoclonal gammopathies and if SFLC could replace the requirement for urine for Bence Jones Protein (BJP) analysis. SFLC were added to consecutive requests for serum electrophoresis (SPE) received to investigate patients for possible B-cell proliferative disorders over a 4 month period. SFLC was measured by immunoturbidimetry (The Binding Site, Birmingham, UK) in 923 patients. Subjects with known B-cell disorders were excluded. Concurrent urine samples were received from 370 patients for BJP(40%). The Hydrasis system was used for SPE, urine electrophoresis (UEP) and urine and serum immunofixation (Sebia, Issy-Les-Moulineaux, France.) Kappa/Lambda FLC ratio was abnormal in 71 (7.7%) patients. In 28 of these cases the SPE showed a possible monoclonal band or hypoglobulinaemia and subsequent serum immunofixation confirmed a monoclonal band in 19. In the remaining 43 with negative SPE but abnormal SFLC ratios, lymphoma was diagnosed in 1, multiple myeloma in 2 and monoclonal gammopathy of undetermined significance in 3. Follow-up is continuing in 3 further patients. Of 15 patients with positive urine BJP, 4 patients had normal SFLC ratios but did not have lymphoproliferative disorders requiring treatment. Additional diagnostic information was gained by adding SFLC to SPE for first line investigation of possible B cell disorders. 6 additional patients were identified by abnormal SFLC ratios. Replacing BJP with SFLC ratio would not have missed any significant pathology. In the light of this study we have adopted SPE and SFLC as our first line tests for the investigation of possible B cell disorders. The quality of our diagnostic service has improved; urine samples were received from only 40% of patients being screened and SFLC analysis allows the more confident exclusion of light chain disorders in the absence of a urine sample. The availability of SFLC results when viewing SPE gels assists in the interpretive process and highlights samples requiring serum immunofixation to identify monoclonal bands in the alph-2 or beta globulin regions or light chain monoclonal bands too small for reliable detection by SPE.