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 kappa/lambda 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 kappa/lambda ratio in which CZE did not demonstrate an M protein. Cases with low free kappa/lambda ratios included 1 chronic lymphocytic leukemia (CLL), 1 IgM lambda with aplastic anemia, and 1 lambda light chain myeloma. Cases with high free kappa/lambda ratios included 2 CLL, 1 lymphocytosis (possibly early CLL), 1 kappa light chain myeloma, 1 atypical lymphoma with neuropathy, and 1 nonsecretory myeloma. Addition of the free kappa/lambda ratio to CZE increases the yield of lymphocyte and plasma cell proliferative processes detected by 56%.

International Myeloma Working Group guidelines for serum-free light chain analysis in multiple myeloma and related disorders

“…1 Serum FLC immunoassays have a sensitivity of less than 1 mg/l. 4 The conclusion drawn from these studies and others 11,[23][24][25][26] is that for the purpose of screening for monoclonal proteins for all diagnoses except AL, the FLC can replace the 24 h urine IFE; however, once a diagnosis of monoclonal gammopathy is made, the 24 h protein IFE should be done. For AL screening, however, the urine IFE should still be done in addition to the serum tests including the serum FLC.…”

Free light chains

“…However, we would like to see no false-negative and no false-positive results when comparing the FREELITE with existing methods for detection of monoclonal proteins. Reports by Beetham et al 9 in this issue (p516--22) and from Hill et al 12 and Bakshi et al 13 all describe 'falsepositive'results with abnormal k/l ratios in the absence of any monoclonal protein or an overt malignant process. The FREELITE approach has been reported to be more sensitive than electrophoresis and immuno¢xa-tion for the detection of free light chains yet 'false-negative' results are reported.…”

“…The FREELITE approach has been reported to be more sensitive than electrophoresis and immuno¢xa-tion for the detection of free light chains yet 'false-negative' results are reported. 9,12,13 The serum FREELITE assay may also show abnormal ratios and when followed up, the patients do have BJP in their urine. 9,12,13 No one system is perfect for every sample arriving in the lab for the investigation of a monoclonal protein.…”

Capillary electrophoresis of proteins 2003–2005

“…Conflicting results between CZE and gel electrophoresis, and interferences of some substances including iodinated contrast agent and antibiotics, have also been observed [197]. Controversial data were also obtained for IgM [198][199][200]: whereas agarose electrophoresis provided a distinct peak in the gamma region of a serum of a patient with IgG l monoclonal gammopathy, CZE could not locate this protein. On the other hand, small monoclonal components of the serum were observed to provide very low biological variation [201].…”