Serum Free Light Chain (FLC) Measurement Can Aid Capillary Zone Electrophoresis in Detecting Subtle FLC-Producing M Proteins

Abstract

We hypothesized that using a free light chain (FLC) assay as an adjunct to capillary zone electrophoresis (CZE) could improve detection of lymphoplasmacytic processes. We prospectively studied 1,003 consecutive serum samples submitted for routine protein electrophoresis and/or immunofixation electrophoresis by CZE and FLC. Samples from patients previously characterized as having M proteins were excluded. Protein electrophoresis was read by a pathologist unaware of the FLC results. Sixteen cases revealed an abnormal free κ/λ ratio in which CZE did not demonstrate an M protein. Nine cases of B-lymphocyte or plasma cell proliferative processes were detected by an abnormal free κ/λ ratio in which CZE did not demonstrate an M protein. Cases with low free κ/λ ratios included 1 chronic lymphocytic leukemia (CLL), 1 IgM λ with aplastic anemia, and 1 λ light chain myeloma. Cases with high free κ/λ ratios included 2 CLL, 1 lymphocytosis (possibly early CLL), 1 κ light chain myeloma, 1 atypical lymphoma with neuropathy, and 1 nonsecretory myeloma. Addition of the free κ/λ ratio to CZE increases the yield of lymphocyte and plasma cell proliferative processes detected by 56%.