Abstract
Serum protein electrophoresis (SPE), urine protein electrophoresis (UPE), and immunofixation (IFE) are routinely used to identify the presence of monoclonal immunoglobulin proteins during the investigation of possible monoclonal gammopathies. The purpose of performing urinary Bence-Jones protein (BJP) analysis is to identify monoclonal light chains in the presence or absence of a serum monoclonal component. These tests may be requested for patients in whom the diagnosis is clinically suspected, or may be initiated as a reflex analysis when the results of other tests suggest that multiple myeloma or plasma cell disorders (PCDs) need to be excluded. The serum free light chain (FLC) assay is a sensitive and quantitative technique for measuring FLC concentrations in serum.1 It has been shown to have greater sensitivity than SPE and IFE and can provide an alternative to BJP analysis.2,3 There are a number of problems associated with detecting monoclonal FLCs in urine. FLCs are filtered through the glomeruli of kidney nephrons, then reabsorbed and metabolised via proximal tubules.4,5 Significant quantities of FLCs do not enter the urine unless the reabsorption capacity of the tubules has been overwhelmed and thus do not necessarily reflect either serum FLC levels or tumour production of monoclonal FLCs. However, the most significant problem with urinalysis in a diagnostic setting is poor compliance with the provision of samples. Hill and colleagues reported ~40%6 while Holding and colleagues7 reported ~17%. Retrospective studies have indicated that the majority of patients with monoclonal gammopathies display abnormal serum FLC ratios/levels at presentation: 100% light chain multiple myeloma,8 82% nonsecretory multiple myeloma,9 96% intact immunoglobulin multiple myeloma,10 and 98% AL amyloidosis.11 In addition, approximately one-third of monoclonal gammopathy of undetermined significance (MGUS) patients display abnormal serum FLC ratios, and these patients have an …
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