Comparison of the Sensitivity of 2 Automated Immunoassays with Immunofixation Electrophoresis for Detecting Urine Bence Jones Proteins

Abstract

Bence Jones proteins [monoclonal free immunoglobulin light chains (FLCs)] are important tumor markers for identifying and managing patients with monoclonal plasma cell diseases, particularly multiple myeloma. In ∼20% of such patients, urine FLCs are the only monoclonal component detected (1)(2)(3)(4). FLCs produced in excess and secreted by a clonal population of plasma cells are excreted into urine in variable amounts as monomers, dimers, polymers, or low–molecular-weight fragments, frequently accompanied by significant quantities of polyclonal FLCs (1)(2)(5)(6)(7). The excretion of monoclonal FLCs varies markedly according to tumor mass, renal function, and the molecular features of the light chains. Furthermore, the clinical significance of FLCs depends on the underlying disease and is assessed in relation to other biochemical, hematologic, clinical, and radiologic data. In particular, urine monoclonal FLCs, often present only at low concentrations, are of considerable clinical significance in the diagnosis of renal disease because of their association with primary (AL) amyloidosis or light chain deposition disease (1)(2)(8). Low concentrations of FLCs are also found in some patients with monoclonal gammopathies of undetermined significance (1)(2). For some years it has been suggested that immunochemical methods for detection of κ and λ immunoglobulin light chains might be useful for detecting urine monoclonal FLCs (9)(10). More recently, immunochemical assays for FLCs have been developed, and 1 study showed that the ratio of urine free κ to λ in combination with urine protein electrophoresis was clinically useful (11). The purpose of our study was to compare the sensitivity of 2 automated nephelometric assays with immunofixation electrophoresis (IFE) for the detection of urinary monoclonal FLCs (12)(13). Between January 2001 and May 2002, we analyzed sera and second-morning urine samples …