American Journal of Hematology / Oncology®
Freelite for Measurement of Urine-Free Light Chains in Monoclonal Gammopathies

Montgomery Lobe, MD, and Donald Pasquale, MD


Monoclonal gammopathies are characterized by pro- duction of monoclonal immunoglobulin heavy or light chains. Historically, the standard for measuring mono- clonal light chains was indirect, requiring 24-hour urine collection, measurement of total protein, and extrapola- tion of light chain concentration using electrophoresis. In 2001, Freelite was developed allowing direct detection of serum-free light chains (FLCs) with sensitivity >2-log higher than immunofixation electrophoresis (IFE), and became standard for diagnosis and monitoring of these disorders. However, cases are missed when urine FLCs are not measured. We studied 23 individuals with mono- clonal gammopathies to determine whether Freelite could be used to measure urine FLCs from a spot urine. We concurrently measured serum and urine FLCs using Freelite and serum heavy chains. Monoclonal urine and serum FLCs correlated in 39% of patients. Both urine and serum monoclonal FLCs correlated with clonal se- rum heavy chains in 25%, serum in only 30%, and urine in only 10%. We conclude that measurement of spot urine FLCs using Freelite may replace 24-hour urine total protein and IFE. While serum FLCs are adequate in most patients, we found a small number of patients for whom urine FLCs outperformed serum FLCs.

AJHO. 2016;12(11):-9-13


Monoclonal gammopathies represent a spectrum of clonal plasma cell disorders that form monoclonal gammopathy of undetermined significance (MGUS) through active multiple myeloma (MM) that are characterized by production of mono- clonal immunoglobulin heavy and/or light chains.1-3 In these disorders, detection of free light chains (FLCs) has been an evolving and, at times, critical analysis for diagnosis, prognosis, and management of treatment.4-8

Historically, the standard for evaluating monoclonal light chain production has been the measurement of urine  excretion of light chains determined by collecting a 24-hour urine speci- men, measuring 24-hour urine total protein, and extrapolating the quantity of light chains using data from a urine protein electrophoresis (UPEP) and immunofixation electrophoresis (IFE).1 In 2001, Freelite was developing the utilization of immu- nonephelometric technology that allowed for improved detec- tion of serum FLCs.9 Sensitivity of UPEP is 500 to 2000   mg/L,
IFE is 150 to 500 mg/L, and Freelite is 1.5 to 3.0 mg/L.10 It     was then demonstrated that serum Freelite alone detected more plasma cell disorders than older methods,7 with the higher detection rate likely due to the increased sensitivity and ability  to measure the ratio of abnormal to normal light  chains.

Serum FLCs utilizing Freelite is now integrated into the standard of care in diagnosis and monitoring of plasma cell disorders. However, this should not replace obtaining urine IFE, as a small number of cases were missed when FLCs were not also measured.1,6 It has been our practice to use Freelite to measure the quantity of FLCs in single urine samples instead  of obtaining a 24-hour urine sample with total protein and  IFE. However, this has not been recommended for routine screening due to paucity of data using this assay for urinary measurements, and due to the concern for possibly confound- ing variable excretion of FLCs because of changes in renal function and variable renal reabsorption and degradation of light chains.10

The goal of this study was to evaluate the utility of using Freelite for measurement of spot urine  FLCs.


This study was approved by the Albany VA Medical Center Institutional Review Board. We identified individuals with the diagnosis of MGUS, smoldering MM (SMM), or MM, who had multiple concurrent measurements of serum and urine FLCs using Freelite, and serum heavy chains (quantitative immuno- globulins). Urine and serum FLCs were measured using Freelite (Binding Site Ltd, Birmingham, UK) by a reference laboratory (Lab Corp, Burlington, NC). All analyses were performed using the involved/monoclonal FLC levels and involved/monoclonal heavy chain levels, when affected. Serum immunoglobulins (immunonephelometry) along with other serum and urine parameters were measured using standard and widely available techniques by the study’s American College of Pathologists accredited medical center chemistry laboratory. Data were analyzed for correlation between parameters using Pearson product-moment correlation. P values < .05 were considered significant.11


Characteristics of the study population are illustrated in Table 1. We identified 23 individuals (all male, consistent with our  vet- eran patient population) with mean (± standard deviation [SD]) age of 71 ± 10.6 years at diagnosis. Five individuals had MGUS,  4 had SMM, and 14  had MM.12 Two of the 14  patients with   MM progressed from MGUS. Twenty-one of 23 patients had intact monoclonal disease, and FLCs were measurable in all 21  of these patients. Two of the 13 patients with MM had light- chain-only disease. A mean (±SD) of 9.2 ± 5.9 matched serum and urine FLC determinations per patient (range, 4–21) was obtained over a mean 17.9 ± 8.4 months. Mean (±SD) serum creatinine of the patients was 1.2 ± 0.4 mg/dL (range,  0.7–2.5). One individual with SMM was excluded from the heavy chain correlations due to insufficient serum FLC  data.

Results of comparisons between immunoglobulin parameters are illustrated in Table 2. Overall, the urine FLCs  correlat- ed with serum FLCs in 9 (39%) individuals, including both patients with light-chain MM. Both urine and serum FLCs cor- related with heavy chain in 5 (25%) patients. Serum FLCs, but not urine FLCs, correlated with serum heavy chain in 6 (30%). Urine FLCs, but not serum FLCs, correlated with heavy chain  in 2 (10%). There was no correlation between urine or serum FLCs with serum heavy chain in 7 (35%) patients. Use of FLC ratio instead of FLCs and “normalization” of urine FLCs based on concurrent urine and serum creatinine determinations did not change any of the correlations in any of the 23   participants (data not shown).

Figure 1 illustrates comparisons between urine and serum FLCs with serum heavy chains in 4 patients. Panels A   and
B illustrate patients for whom both urine and serum FLCs correlate with serum heavy chain; Panel C illustrates an individual for whom only the serum FLCs correlated with the serum heavy chain; and Panel D illustrates an individual for whom only the urine FLCs correlated with the serum heavy chain. Figure 2 illustrates 2 patients for whom the urine FLCs correlated with the serum FLCs.


Due to its greater sensitivity in the detection of monoclonal immunoglobulins, serum FLCs have become important  for diagnosis, prognosis, and management of plasma-cell disor-  ders. This method is incorporated into current guidelines for assessing patients with monoclonal gammopathies. However, measurement of urine FLCs continues to be required because a small number of individuals are detected only by measurement of urine FLC  excretion.1,6

Methodology for measuring urine FLCs continues to be collecting 24-hour urine specimen and extrapolating the  quantity of light chains excreted based on urine IFE.1,4 This process is subject to error when collection is incomplete, and  the sensitivity of IFE is about 2-log less than the Freelite assay. Use of Freelite for measurement of urine FLCs has not been promoted because of a paucity of data using this method, and because of concern regarding using a spot urine due to variabil- ity in renal function and tubular handling of light   chains,10,13 with prior studies failing to show association between urine FLCs and serum FLCs.4,8,13 We also failed to show association with aggregated data. However, there was a clear association in 39% of patients between the serum and urine FLCs, and clear associations in 25% of patients between urine FLCs and serum heavy chain. We did not specifically compare head-to-head measurement of spot urine FLCs using Freelite with 24-hour collection quantitation via IFE; however, we feel that with the 2-log increased sensitivity of Freelite, Freelite will outperform IFE. We also observed a small but defined minority of patients for whom urine FLCs outperformed serum  FLCs.

Use of Freelite as an assay for immunoglobulin light chains does not substitute for urinalysis to screen for albuminuria, which may be an indication of renal light-chain amyloid. If proteinuria is indicated on the screening urinalysis, a 24-hour urine collection should be considered to determine the quantity of albumin as a part of an evaluation for amyloid   disease.

We feel that due to the increased (2-log) sensitivity of Freelite over IFE, the ability to quantitate the kappa-to-lambda light chain ratio as an indication of clonality, and the convenience   of a spot urine over a 24-hour collection, this assay is a valid alternative to the currently promoted  methodology.


The measurement of urine FLCs from a single urine collection using the Freelite assay is a convenient and valid tool, and   in
a minority of patients with monoclonal gammopathies, it adds unique information about disease activity.
Author affiliations: Montgomery Lobe, MD, is from the Department of Medicine, Albany Medical College, Albany,  NY; Donald Pasquale, MD, is from the Medical VA Care Line, Stratton VA Medical Center,  Albany.
Author disclosures: The authors report no relevant conflicts of interest.
Address correspondence to: Donald Pasquale, MD, Medical  VA Care Line, Stratton VA Medical Center, 113 Holland Avenue, Albany, New York 12208; email: Author contributions: Dr. Pasquale designed the study. Dr. Lobe collected data. Drs. Pasquale and Lobe analyzed the data and wrote the manuscript.
Supported by: Department of Veterans  Affairs


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