Monoclonal free light chains in urine and their significance in clinical diagnostics: are they really tumor markers?

Ratio of urinary free immunoglobulin light chain kappa to lambda in the diagnosis of Bence Jones proteinuria

The aim of this study was to evaluate the diagnostic efficacy of the ratio of urinary free light chain (FLC) kappa to lambda (kappa/lambda ratio) for the detection of Bence Jones protein (BJP). Urine specimens were collected from 243 patients suspected of having BJP. Immunofixation identified 59 BJP-positive specimens among them. The kappa/lambda ratios of all specimens were determined by FLC immunoassays and then the cut-offs for the kappa/lambda ratio were defined as 5.5 for BJP K and 0.1 for BJP lambda by ROC curve analyses. Using the cut-offs, we detected abnormal kappa/lambda ratios in 51 (86%) of the 59 BJP-positives and 11 (6%) of the 184 BJP-negatives identified by the results of immunofixation. High-resolution urinary protein electrophoresis (UPE), a sensitive method for BJP screening, showed almost equal sensitivity to the kappa/lambda ratio, detecting monoclonal band(s) in 52 (88%) of the 59 BJP-positives. However, in UPE analysis these positive specimens should be followed by redundant immunofixation analysis to determine the isotypes. We further evaluated the combination method of FLC assays with UPE that correctly diagnosed 82% of the specimens as positive or negative for BJP, with only two false-negative results. These results suggest that quantitative FLC immunoassays provide an alternative or complementary method for the detection of BJP.

Electrophoretic analysis of Bence Jones proteinuria

The electrophoresis of Bence Jones proteinuria (BJP) by urinary protein electrophoresis (UPE), immunoelectrophoresis (IE), immunofixation electrophoresis (IFE), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing (IEF), two-dimensional electrophoresis (2-DE) and capillary electrophoresis (CE) is described. UPE, IE and IFE are briefly discussed as clinical laboratory methods for the detection and typing of free light chain (LC) whilst the high resolution electrophoretic methods (SDS-PAGE, IEF, 2-DE and CE) are considered in greater detail as research tools for molecular characterisation of free LC and its association with nephrotoxicity. Refinements of sample processing designed to improve the standardisation of analysis of BJP by high resolution electrophoretic methods are reported.

Clinical analysis of human urinary proteins using high resolution electrophoretic methods

The application of isoelectric focusing (IEF), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional electrophoresis (2-DE) and capillary electrophoresis (CE) for high resolution electrophoretic analysis of human urinary proteins is reviewed. In each case, the information is tabulated chronologically with details of sample preparation, electrophoretic system, detection method and clinical application. The text includes an historical perspective of the use of each method for urinalysis and a detailed review of the application of the methods to the investigation of renal disease, renal transplantation, Bence Jones proteinuria (BJP), diabetes mellitus, cadmium toxicity, nephrolithiasis and cancers of the urogenital tract.

Clinical applications of immunoglobulin free light chain estimations

The relevance of free light chain assays to diagnosis, staging, treatment and prognosis assessment in B-cell disorders (including myeloma, chronic lymphocytic leukaemia, and lymphoma), multiple sclerosis and diabetes is discussed and their actual and potential use is examined.