Use of nonclonal serum immunoglobulin free light chains to predict overall survival in the general population.

OBJECTIVE: To determine whether the free light chain (FLC) assay provides prognostic information relevant to the general population. METHODS: After excluding persons with a known plasma cell disorder, we studied 15,859 Olmsted County, Minnesota, residents 50 years or older in whom unmasked data and samples for FLC testing were available. Baseline information was obtained between March 13, 1995, and November 21, 2003, and follow-up status and cause of death were identified through June 30, 2009. The κ and λ FLC sum (Σ FLC) was evaluated for its ability to predict overall survival. Specific causes of death were also investigated. RESULTS: In 158,003 person-years of follow-up, 4348 individuals died. A high Σ FLC was significantly predictive of worse overall survival; the risk ratio for death for those with the highest decile of Σ FLC (ie, ≥ 4.72 mg/dL) was 4.4 (95% confidence interval, 4.1-4.7) relative to the remaining study participants. Multivariate analyses demonstrated that this excess risk of death was independent of age, sex, and renal insufficiency, with a corrected risk ratio of 2.1 (95% confidence interval, 1.9-2.2). The increased mortality was not restricted to any particular cause of death because the observed-to-expected risk of death from most causes was significantly higher among those individuals with an antecedent Σ FLC of 4.72 mg/dL or higher, which is near the upper limit of normal for the test. CONCLUSION: A nonclonal elevation of Σ FLC is a significant predictor of worse overall survival in the general population of persons without plasma cell disorders.

Serum free light chain immunoassay as an adjunct to serum protein electrophoresis and immunofixation electrophoresis in the detection of multiple myeloma and other B-cell malignancies.

BACKGROUND: Protein and immunofixation electrophoresis of serum and urine are established as diagnostic aids for identifying monoclonal gammopathies. However, many patient sera sent to laboratories are not accompanied by urine samples and recent reports suggest the use of serum free light chain (sFLC) analysis in combination with serum protein electrophoresis (SPE) and immunofixation electrophoresis (lFE) could eliminate the need for urinalysis. The aim of the study was to assess the utility of sFLC measurement in addition to serum protein electrophoresis in the identification of patients with B-cell malignancies. METHODS: A total of 952 serum samples were analysed by serum protein electrophoresis and those with abnormal bands were analysed by immunofixation. sFLCs were measured in a retrospective manner by automated assay. RESULTS: In our study of 952 patient sera, it was found that FLC analysis identified 23 additional cases of B-cell malignancies which were missed by SPE. CONCLUSIONS: The additional malignancies identified by sFLC analysis add support for its inclusion in the routine screening protocol for B-cell malignancies.

Assessment of monoclonal gammopathies by nephelometric measurement of individual immunoglobulin kappa/lambda ratios.

BACKGROUND: Currently, monoclonal immunoglobulins are identified and quantified from bands on electrophoretic gels. As an alternative, clonality might be determined by measuring the separate light chain types of each Ig class to allow numerical assessment of Ig'kappa/Ig'lambda ratios, analogous to free light chain kappa/lambda ratios. METHODS: Using immunization, tolerization, and adsorption procedures, we prepared sheep antibodies against each of the 6 separate molecules, IgGkappa, IgGlambda, IgAkappa, IgAlambda, IgMkappa, and IgMlambda. Antibody targets comprised the junctional epitopes between the heavy chain and light chain domains. After purification, we assessed the antisera on a Siemens Dade-Behring BN II nephelometer for analytical quality and clinical utility. RESULTS: High-avidity, specific antibodies allowed the production of automated nephelometric immunoassays for each Ig light chain type. Laboratory comparison with serum protein electrophoresis, using dilution experiments, showed lower analytical sensitivity for monoclonal IgG detection but similar or greater sensitivity for IgA and IgM, particularly when the monoclonal bands overlaid transferrin. Results obtained from typing of monoclonal proteins into IgG, A, or M types were comparable with results obtained by immunofixation-electrophoresis methods. Initial clinical studies, in multiple myeloma patients, indicated that Ig'kappa/Ig'lambda ratios were sometimes more sensitive than immunofixation electrophoresis, provided numerical results, and correlated with changes in disease. CONCLUSIONS: Immunoassays for intact Ig kappa/lambda pairs are possible and should assist in the management of patients with monoclonal gammopathies.

Quantitative assessment of serum and urinary polyclonal free light chains in patients with chronic kidney disease.

BACKGROUND AND OBJECTIVES: Monoclonal free light chains (FLC) frequently cause kidney disease in patients with plasma cell dyscrasias. Polyclonal FLC, however, have not been assessed in patients with chronic kidney disease (CKD) yet could potentially play an important pathologic role. This study describes for the first time polyclonal FLC in patients with CKD. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: A sensitive, quantitative immunoassay was used to analyze serum and urinary polyclonal FLC in 688 patients with CKD of various causes. RESULTS: Serum kappa and lambda FLC concentrations increased progressively with CKD stage (both P < 0.001) and strongly correlated with markers of renal function, including cystatin-C (kappa: R = 0.8, P < 0.01; and lambda: R = 0.79, P < 0.01). Urinary FLC concentrations varied significantly between disease groups (kappa: P < 0.001; lambda: P < 0.005) and also rose significantly with increasing CKD stage (both FLC P < 0.0001). Urinary FLC concentrations were positively correlated with their corresponding serum concentration (kappa: R = 0.63; lambda: R = 0.65; both P < 0.001) and urinary albumin creatinine ratio (kappa: R = 0.58; lambda: R = 0.65; both P < 0.001). The proportion of patients with abnormally high urinary FLC concentrations rose with both the CKD stage and the severity of albuminuria. CONCLUSIONS: This study demonstrates significant abnormalities of serum and urinary polyclonal FLC in patients with CKD. These data provide the basis for studies that assess the contribution of polyclonal FLC to progressive renal injury and systemic inflammation in patients with kidney disease.

Quantitative assessment of serum and urinary polyclonal free light chains in patients with type II diabetes: an early marker of diabetic kidney disease?

OBJECTIVE: Free light chains (FLCs) are bi-products of normal immunoglobulin synthesis and are predominately removed from the circulation by the kidneys. This study assessed polyclonal FLCs as a novel biomarker of early diabetic kidney disease. RESEARCH DESIGN/METHODS: Serum and urinary FLCs were assessed by the immunoassay Freelite, in white and South-Asian patients with type II diabetes recruited from the United Kingdom Asian Diabetes Study. RESULTS: The incidence of monoclonal proteins in this diabetic population was 1.9%. Type II diabetic patients had significantly raised concentrations of serum polyclonal FLCs before overt renal impairment developed (p < 0.001). Both kappa and lambda FLCs correlated with all tested markers of renal function; in particular cystatin-C: Spearman's coefficient (R) = 0.55 (p < 0.01) and R = 0.56 (p < 0.01), respectively. The South-Asian diabetic patients had higher serum polyclonal FLCs than Caucasian diabetic patients and this was independent of renal function. Urinary FLCs concentrations were raised in diabetic patients (p < 0.001). The majority (68%) of diabetic patients with normal urinary albumin:creatinine ratios (ACRs) had abnormal urinary FLC:creatinine ratios. Both kappa and lambda FLC concentrations correlated with urinary ACR: R = 0.32, p < 0.01 and R = 0.25, p < 0.01 respectively. CONCLUSIONS: Type II diabetic patients can have significantly raised concentrations of serum and urinary polyclonal FLCs before overt renal disease occurs. These novel findings provide the basis for future studies to assess whether polyclonal FLCs could provide a useful tool for early diagnosis of diabetic kidney disease.

Efficient removal of immunoglobulin free light chains by hemodialysis for multiple myeloma: in vitro and in vivo studies.

Of patients with newly diagnosed multiple myeloma, approximately 10% have dialysis-dependent acute renal failure, with cast nephropathy, caused by monoclonal free light chains (FLC). Of these, 80 to 90% require long-term renal replacement therapy. Early treatment by plasma exchange reduces serum FLC concentrations, but randomized, controlled trials have shown no evidence of renal recovery. This outcome can be explained by the low efficiency of the procedure. A model of FLC production, distribution, and metabolism in patients with myeloma indicated that plasma exchange might remove only 25% of the total amount during a 3-wk period. For increasing FLC removal, extended hemodialysis with a protein-leaking dialyzer was used. In vitro studies indicated that the Gambro HCO 1100 dialyzer was the most efficient of seven tested. Model calculations suggested that it might remove 90% of FLC during 3 wk. This dialyzer then was evaluated in eight patients with myeloma and renal failure. Serum FLC reduced by 35 to 70% within 2 hr, but reduction rates slowed as extravascular re-equilibration occurred. FLC concentrations rebounded on successive days unless chemotherapy was effective. Five additional patients with acute renal failure that was caused by cast nephropathy then were treated aggressively, and three became dialysis independent. A total of 1.7 kg of FLC was removed from one patient during 6 wk. Extended hemodialysis with the Gambro HCO 1100 dialyzer allowed continuous, safe removal of FLC in large amounts. Proof of clinical value now will require larger studies.

The tumor kinetics of multiple myeloma following autologous stem cell transplantation as assessed by measuring serum-free light chains.

In multiple myeloma, changes in serum-free immunoglobulin light chains (FLC) are a more rapid indicator of treatment response than intact immunoglobulin due to their shorter serum half-life. The present study analysed the changes in serum FLC after autologous peripheral blood stem cell transplantation (PBSCT) in 19 patients. The majority of myeloma patients (18 of 19) undergoing PBSCT had a rapid fall in FLC concentrations. In all 11 of 19 patients with raised tumor FLC, it fell within 48 h following high-dose melphalan. In patients with monoclonal intact immunoglobulin, the tumor FLC fell quicker (median half-life 4.3 days) than the monoclonal intact immunoglobulin (median half-life 14 days). FLC recovery occurred after (13 of 19) or around the time of neutrophil engraftment (6 of 19). With a median follow up of 220 days post-transplant, 16 of 19 patients have a normal FLC ratio and 3 of 19 have an elevated tumor FLC/abnormal ratio. FLC assays provided a sensitive monitor of changes in tumor and non-tumor plasma cells after PBSCT. This assay is potentially valuable as a marker of chemosensitivity, as an indicator of residual tumor and indicated time to lymphocyte engraftment. Further follow-up is required to ascertain whether differences in the kinetics of FLC responses have any prognostic clinical utility.

Serum test for assessment of patients with Bence Jones myeloma.

Bence Jones protein in urine (immunoglobulin free-light-chains) is characteristic of light-chain multiple myeloma. We aimed to compare a quantitative immunoassay for serum free-light-chains with urine tests. Of 224 patients with light-chain myeloma tested at entry to clinical trials, all were correctly identified from serum samples. During monitoring of 82 patients, changes in serum and urine free-light-chains corresponded, but urine became negative for free-light-chains in 26 patients, whereas it remained abnormal in serum in 73 patients. Serum assays could replace Bence Jones protein urine tests for patients with light-chain multiple myeloma.