title: Clinical significance of abnormal serum free light chain ratio: diagnostic confusion or underlying monoclonality?
abstract: BACKGROUND
  The spectrum of laboratory tests used to detect monoclonal components (M-components) include serum and urine protein electrophoresis (PEP), immunofixation electrophoresis, and immunonephelometric methods such as free light chain assay (sFLC).
  
  
  METHODS
  In this study, we retrospectively analyzed 78 patients who were to be tested with FLC without previous evidence of MG in order to investigate the clinical meaning of K/L screening. Abnormal K/L in sFLC was found in 25 samples from 21 patients (21/78, 26.92%).
  
  
  RESULTS
  Among them, serum electrophoresis was requested for 16 patients where 5 were diagnosed as either normal or polyclonal gammopathy, 5 as plasma cell myeloma, 5 as monoclonal gammopathy of undetermined significance and I as amyloidosis. In total, 11 patients were revealed to have MG related diseases (11/25, 44.0 %).
  
  
  CONCLUSIONS
  The clinical function of sFLC as a MG screening tool turned out to be effective based on the result where 16 out of 21 patients who were subject to further study led to diagnoses of MG related diseases in 11 patients. To provide an accurate evaluation for the performance of sFLC as a screening tool for MG, further studies should include additional confirmation of PEP results for patient groups that showed normal K/L ratios.
authors.affiliation: Department of Laboratory Medicine, Kyung Hee University, School of Medicine, Seoul, Korea.
authors.forename: Sun Young
authors.initials: SY
authors.lastname: Cho
authors.affiliation: Department of Biomedical Science, Kyung Hee University Graduate School, Seoul, Korea.
authors.forename: You Sun
authors.initials: YS
authors.lastname: Nam
authors.affiliation: Department of Hematology-Oncology, Kyung Hee University, School of Medicine, Seoul, Korea.
authors.forename: Hwi-Joong
authors.initials: HJ
authors.lastname: Yoon
authors.affiliation: Department of Laboratory Medicine, Kyung Hee University, School of Medicine, Seoul, Korea.
authors.forename: Hee Joo
authors.initials: HJ
authors.lastname: Lee
authors.affiliation: Department of Laboratory Medicine, Kyung Hee University, School of Medicine, Seoul, Korea.
authors.forename: Tae Sung
authors.initials: TS
authors.lastname: Park
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000097:blood*; D008297:Male; D008875:Middle Aged; D010265:Paraproteinemias / Q000097:blood / Q000175:diagnosis*
chemical_list: D007147:Immunoglobulin Light Chains