title: Serum Free Light Chain Assay and κ/λ Ratio Performance in Patients Without Monoclonal Gammopathies:  High False-Positive Rate.
abstract: OBJECTIVE
  Serum free light chain assay is a recommended screening test for monoclonal gammopathies. Anecdotal observations indicated a high rate of false-positive abnormal κ/λ ratios. This study was undertaken to ascertain the magnitude of the false-positive rate and factors contributing to the error rate.
  
  
  METHODS
  Results of serum protein electrophoresis, serum free light chains, and related tests, usually done for investigation of suspected monoclonal gammopathy, were reviewed retrospectively for 270 patients and 297 observations.
  
  
  RESULTS
  Using the conventional κ/λ ratio, 36.4% of the ratios were abnormal, in the absence of monoclonal gammopathy. When the renal κ/λ ratio was used, the rate of abnormal κ/λ ratios was 30.1%. In patients with a γ-globulin concentration of 1.6 g/dL or more, the usual κ/λ ratio was abnormal in 54.8% of the patients. Urine protein electrophoresis was used in 53 (19.6%) instances, whereas bone marrow examination was done in 65 (24.1%) cases.
  
  
  CONCLUSIONS
  Usual κ/λ ratio was abnormal in 36.4% of the observations in patients without evidence of monoclonal gammopathy, and an abnormal κ/λ ratio should not be used as the sole indicator for diagnosis of neoplastic proliferation of the lympho-plasmacytic system. Hypergammaglobulinemia is associated with a higher rate of false-positive abnormal κ/λ ratios. Examination of urine for monoclonal immunoglobulins may be underused, and recommendations by some to use serum free light chain assay in place of, rather than as an adjunct to, urine electrophoresis are not warranted.
authors.affiliation: From the Department of Pathology, Division of Clinical Pathology, Augusta University, Medical College of Georgia, Augusta. gurmukhsinghmdphd@yahoo.com.
authors.forename: Gurmukh
authors.initials: G
authors.lastname: Singh
mesh_terms: D005189:False Positive Reactions; D006801:Humans; D007145:Immunoglobulin kappa-Chains / Q000097:blood*; D007146:Immunoglobulin lambda-Chains / Q000097:blood*; D010265:Paraproteinemias / Q000175:diagnosis*; D012189:Retrospective Studies
chemical_list: D007145:Immunoglobulin kappa-Chains; D007146:Immunoglobulin lambda-Chains
keywords: Monoclonal gammopathy; Multiple myeloma; Protein electrophoresis; Serum free light chain assay; Serum free light chains; Serum protein electrophoresis; Serum protein immunofixation electrophoresis; Urine protein electrophoresis; Urine protein immunofixation electrophoresis; ratio; κ/λ