title: Diagnostic performance of quantitative kappa and lambda free light chain assays in clinical practice.
abstract: BACKGROUND
  The quantitative assay for free light chains (FLCs) is a recently introduced commercial test reported to be sensitive and specific for detecting FLC diseases such as primary systemic amyloidosis (AL), light chain deposition disease (LCDD), nonsecretory multiple myeloma (NSMM), and light chain multiple myeloma. We evaluated its diagnostic performance in clinical practice.
  
  
  METHODS
  All FLC clinical test results generated in 2003 were abstracted from the Laboratory Information System. Diagnoses were obtained from the Dysproteinemia database and the patient medical history.
  
  
  RESULTS
  In 2003, we received samples for FLC assays from 1020 Mayo Clinic patients. The majority of these patients (88%) had bone marrow-derived monoclonal plasma cell disorders (PCDs). The 121 patients who did not have monoclonal gammopathy all had FLC kappa/lambda ratios within the range of values obtained for a reference population in our laboratory. Among the patients with monoclonal gammopathies were patients with multiple myeloma (330), AL (269), monoclonal gammopathy of undetermined significance (114), smoldering multiple myeloma (72), plasmacytoma (22), NSMM (20), macroglobulinemia (9), LCDD (7), and a variety of other PCDs. Among the 110 AL patients who had not been previously treated and who had a FLC assay performed within 120 days of diagnosis, the FLC kappa/lambda ratio was positive in 91% compared with 69% for serum immunofixation electrophoresis (IFE) and 83% for urine IFE. The combination of serum IFE and serum FLC assay detected an abnormal result in 99% (109 of 110) of patients with AL.
  
  
  CONCLUSIONS
  The performance of the FLC assay in this analysis of clinical laboratory data is consistent with results from published retrospective validation studies.
authors.affiliation: Division of Clinical Biochemistry and Immunology, Department of Laboratory Medicine and Pathology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA. katzmann@mayo.edu
authors.forename: Jerry A
authors.initials: JA
authors.lastname: Katzmann
authors.forename: Roshini S
authors.initials: RS
authors.lastname: Abraham
authors.forename: Angela
authors.initials: A
authors.lastname: Dispenzieri
authors.forename: John A
authors.initials: JA
authors.lastname: Lust
authors.forename: Robert A
authors.initials: RA
authors.lastname: Kyle
mesh_terms: D000686:Amyloidosis / Q000175:diagnosis*; D002984:Clinical Laboratory Information Systems; D006801:Humans; D007145:Immunoglobulin kappa-Chains / Q000097:blood*; D007146:Immunoglobulin lambda-Chains / Q000097:blood*; D007755:Laboratories, Hospital; D016347:Medical Records Systems, Computerized; D009101:Multiple Myeloma / Q000175:diagnosis; D010265:Paraproteinemias / Q000175:diagnosis*; D010954:Plasmacytoma / Q000175:diagnosis; D008258:Waldenstrom Macroglobulinemia / Q000175:diagnosis
chemical_list: D007145:Immunoglobulin kappa-Chains; D007146:Immunoglobulin lambda-Chains