Serum Free Light Chain (FLC) Measurement Can Aid Capillary Zone Electrophoresis in Detecting Subtle FLC-Producing M Proteins

Retrospective Analysis of Serum Free Light Chain Reference Intervals and Risk for Monoclonal Gammopathy Suggests Different Limits Than Those in International Guidelines

OBJECTIVES

Recent reference interval studies of the serum free light chain (FLC) test using contemporary instruments display divergence with the diagnostic range generally adopted as the international standard. In this study, we perform a retrospective reference interval analysis with risk predictions for monoclonal gammopathy.

METHODS

Retrospective laboratory and clinical data for 8,986 patients were included in the study. Reference intervals were generated against a set of inclusion/exclusion criteria for two time periods representing the use of different instruments. The presence of monoclonal gammopathy was established from diagnostic test interpretations and EHR diagnosis codes in the patient problem lists and medical history.

RESULTS

The 95% FLC ratio reference intervals were 0.76-2.38 for SPAPLUS®, and 0.68-1.82 for Optilite® instruments. These intervals varied considerably from the current diagnostic range of 0.26-1.65 and mapped approximately to the FLC ratios beyond which risk of monoclonal gammopathy substantially increased.

CONCLUSIONS

These findings corroborate recent reference interval studies and support recommendations for independent re-evaluation of intervals by institutions as well as an update of international guidelines.

A Cohort Study of Free Light Chain Ratio in Combination with Serum Protein Electrophoresis as a First-Line Test in General Practice

Simple Summary

Multiple Myeloma (MM) can be a diagnostic challenge as it often presents with unspecific symptoms in patients in general practice. Serum-free light chain (sFLC) ratio is suggested to replace urine protein electrophoresis (UPE) in the diagnostic work-up of myeloma. We aimed to investigate the performance of the sFLC ratio in general practice (GP) compared to UPE in a low prevalence cohort of 13,210 patients from general practice. We found that sFLC ratio performs in line with UPE; however, we observed a pronounced number of false-positive tests. Therefore, local instrument-dependent adjustment of reference ranges/decision limits should be considered to avoid an unnecessarily high number of false-positive tests.

Abstract

Multiple Myeloma (MM) often present with unspecific symptoms, which can lead to diagnostic delay. Serum-free light chain (sFLC) ratio is suggested to replace urine protein electrophoresis (UPE) in the diagnostic work-up of myeloma. We aimed to investigate the performance of the sFLC-ratio in general practice (GP) compared to UPE, just as we explored different sFLC-ratio cut-offs’ influence on diagnostic values. In a cohort of 13,210 patients from GP measures of sFLC-ratio, serum protein electrophoresis (SPE), or UPE were compared to diagnoses of incident M-component related diseases acquired from Danish health registers. UPE and sFLC-ratio equally improved diagnostic values when combined with SPE (sensitivity: SPE and UPE: 95.6 (90.6–98.4); SPE and sFLC-ratio: 95.1 (90.2–98.0)). The addition of the sFLC-ratio to SPE resulted in the identification of 13 patients with MGUS, light chain disease and amyloidosis, which was in line with the addition of UPE to SPE. The number of false-positive tests was UPE and SPE: 364 (11%) and sFLC-ratio and SPE: 677(19%). Expanding sFLC-ratio reference range to 0.26–4.32 resulted in a significant reduction in false positives n = 226 (6%) without loss of patients with clinical plasma cell dyscrasias. sFLC-ratio improves the diagnostic value of SPE in GP. However, due to low specificity and a large number of false positives, expanded cut-off values should be considered.

Evaluation of two serum free light chain quantitation methods, Freelite and Seralite, in the clinical laboratory with a view to switching immunoassay

BACKGROUND

Serum free light chain (sFLC) quantitation is central for plasma cell dyscrasias. Several assays are available and switching sFLC methods may be advantageous in certain laboratories. This study performed Freelite and Seralite simultaneously for samples received by the clinical laboratory over a 10 month period and compared quantitation and its impact on interpretation of patient results.

METHODS

Patients (N = 189) included multiple myeloma (MM) and related plasma cell cancers, monoclonal gammopathy of unknown significance (MGUS), AL amyloidosis and renal impairment. sFLC quantitation and clinical agreement was assessed between methods.

RESULTS

Clinical agreement was substantial at diagnosis (κ = 0.647, p < .01) and moderate for monitoring (κ = 0.591, p < .01). Good concordance was seen for MM and related plasma disorders and MGUS, with poorer agreement seen for AL amyloidosis. Case studies illustrated agreement in pattern of myeloma disease activity. Bland-Atman plots showed small mean bias but increasing variation between methods with increasing FLC concentrations. Passing-Bablok analysis confirmed systematic differences in quantitation between methods.

CONCLUSIONS

Despite differences in quantitation, overall, agreement was seen between the different sFLC platforms in relation to the clinical interpretation. As a rapid test without the need for large and expensive analysers, Seralite may be highly applicable in certain laboratories to enable in-house testing.

Isolation of Circulating Plasma Cells in Multiple Myeloma Using CD138 Antibody-Based Capture in a Microfluidic Device

The necessity for bone marrow aspiration and the lack of highly sensitive assays to detect residual disease present challenges for effective management of multiple myeloma (MM), a plasma cell cancer. We show that a microfluidic cell capture based on CD138 antigen, which is highly expressed on plasma cells, permits quantitation of rare circulating plasma cells (CPCs) in blood and subsequent fluorescence-based assays. The microfluidic device is based on a herringbone channel design, and exhibits an estimated cell capture efficiency of ~40–70%, permitting detection of <10 CPCs/mL using 1-mL sample volumes, which is difficult using existing techniques. In bone marrow samples, the microfluidic-based plasma cell counts exhibited excellent correlation with flow cytometry analysis. In peripheral blood samples, the device detected a baseline of 2–5 CD138⁺ cells/mL in healthy donor blood, with significantly higher numbers in blood samples of MM patients in remission (20–24 CD138⁺ cells/mL), and yet higher numbers in MM patients exhibiting disease (45–184 CD138⁺ cells/mL). Analysis of CPCs isolated using the device was consistent with serum immunoglobulin assays that are commonly used in MM diagnostics. These results indicate the potential of CD138-based microfluidic CPC capture as a useful ‘liquid biopsy’ that may complement or partially replace bone marrow aspiration.

Serum Free Light Chain Assay and κ/λ Ratio Performance in Patients Without Monoclonal Gammopathies: High False-Positive Rate

OBJECTIVES

Serum free light chain assay is a recommended screening test for monoclonal gammopathies. Anecdotal observations indicated a high rate of false-positive abnormal κ/λ ratios. This study was undertaken to ascertain the magnitude of the false-positive rate and factors contributing to the error rate.

METHODS

Results of serum protein electrophoresis, serum free light chains, and related tests, usually done for investigation of suspected monoclonal gammopathy, were reviewed retrospectively for 270 patients and 297 observations.

RESULTS

Using the conventional κ/λ ratio, 36.4% of the ratios were abnormal, in the absence of monoclonal gammopathy. When the renal κ/λ ratio was used, the rate of abnormal κ/λ ratios was 30.1%. In patients with a γ-globulin concentration of 1.6 g/dL or more, the usual κ/λ ratio was abnormal in 54.8% of the patients. Urine protein electrophoresis was used in 53 (19.6%) instances, whereas bone marrow examination was done in 65 (24.1%) cases.

CONCLUSIONS

Usual κ/λ ratio was abnormal in 36.4% of the observations in patients without evidence of monoclonal gammopathy, and an abnormal κ/λ ratio should not be used as the sole indicator for diagnosis of neoplastic proliferation of the lympho-plasmacytic system. Hypergammaglobulinemia is associated with a higher rate of false-positive abnormal κ/λ ratios. Examination of urine for monoclonal immunoglobulins may be underused, and recommendations by some to use serum free light chain assay in place of, rather than as an adjunct to, urine electrophoresis are not warranted.

Audit of Use and Overuse of Serum Protein Immunofixation Electrophoresis and Serum Free Light Chain Assay in Tertiary Health Care: A Case for Algorithmic Testing to Optimize Laboratory Utilization

OBJECTIVES

Overuse of laboratory tests is a persistent issue. We examined the use and overuse of serum immunofixation electrophoresis and serum free light chain assays to develop an algorithm for optimizing utilization.

METHODS

A retrospective review of all tests, for investigation of monoclonal gammopathies, for all patients who had any of these tests done from April 24, 2014, through July 25, 2014, was carried out. The test orders were categorized as warranted or not warranted according to criteria presented in the article.

RESULTS

A total of 237 patients were tested, and their historical records included 1,503 episodes of testing for one or more of serum protein electrophoresis, serum immunofixation electrophoresis, and serum free light chain assays. Only 46% of the serum immunofixation and 42% serum free light chain assays were warranted. Proper utilization, at our institution alone, would have obviated $64,182.95/year in health care costs, reduced laboratory cost of reagent alone by $26,436.04/year, and put $21,904.92/year of part B reimbursement at risk.

CONCLUSIONS

Fewer than half of the serum immunofixation and serum free light chain assays added value. The proposed algorithm for testing should improve utilization. Risk to part B billing may be a disincentive to reducing test utilization.

Serum free light chain assays not total light chain assays are the standard of care to assess Monoclonal Gammopathies

The diagnosis of Multiple Myeloma is a challenge to the physician due to the non-specific symptoms (anemia, bone pain and recurrent infections) that are commonplace in the elderly population. However, early diagnosis is associated with less severe disease, including fewer patients presenting with acute renal injury, pathological fractures and severe anemia. Since 2006, the serum free light chain test Freelite(®) has been included alongside standard laboratory tests (serum and urine protein electrophoresis, and serum and urine immunofixation) as an aid in the identification of monoclonal proteins, which are a cornerstone for the diagnosis of Multiple Myeloma. The serum free light chain assay recognizes the light chain component of the immunoglobulin in its free form with high sensitivity. Other assays that measure light chains in the free and intact immunoglobulin forms are sensitive, but unfortunately, due to the nomenclature used, these assays (total light chains) are sometimes used in place of the free light chain assay. This paper reviews the available literature comparing the two assays and tries to clarify hypothetical limitations of the total assay to detect Multiple Myeloma. Furthermore, we elaborate on our study comparing the two assays used in 11 Light Chain Multiple Myeloma patients at presentation and 103 patients taken through the course of their disease. The aim of this article is to provide a clear discrimination between the two assays and to provide information to physicians and laboratory technicians so that they can utilize the International Myeloma Working Group guidelines.

Laboratory testing requirements for diagnosis and follow-up of multiple myeloma and related plasma cell dyscrasias

Monoclonal immunoglobulins are markers of plasma cell proliferative diseases and have been described as the first (and perhaps best) serological tumor marker. The unique structure of each monoclonal protein makes them highly specific for each plasma cell clone. The difficulties of using monoclonal proteins for diagnosing and monitoring multiple myeloma, however, stem from the diverse disease presentations and broad range of serum protein concentrations and molecular weights. Because of these challenges, no single test can confidently diagnose or monitor all patients. Panels of tests have been recommended for sensitivity and efficiency. In this review we discuss the various disease presentations and the use of various tests such as protein electrophoresis and immunofixation electrophoresis as well as immunoglobulin quantitation, free light chain quantitation, and heavy-light chain quantitation by immuno-nephelometry. The choice of tests for inclusion in diagnostic and monitoring panels may need to be tailored to each patient, and examples are provided. The panel currently recommended for diagnostic screening is serum protein electrophoresis, immunofixation electrophoresis, and free light chain quantitation.

Challenges of measuring monoclonal proteins in serum

The measurement of monoclonal protein (M-protein) is vital for stratifying risk and following individuals with a variety of monoclonal gammopathies. Direct measurement of the M-protein spike by electrophoresis and immunochemical measurements of specific isotypes or free light chains pairs has provided useful information about the quantity of M-protein. Nonetheless, both traditional electrophoresis and immunochemical methods give poor quantification with M-proteins smaller than 10 g/L (1 g/dL) when in the presence of polyclonal immunoglobulins that co-migrate with the M-protein. In addition, measurements by electrophoresis of M-proteins migrating in the β- and α-regions are contaminated by normal serum proteins in those regions. The most precise electrophoretic method to date for quantification involves exclusion of the polyclonal immunoglobulins by using the tangent skimming method on electropherograms, which provides a 10-fold improvement in precision. So far, however, tangent measurements are limited to γ migrating M-proteins. Another way to improve M-protein measurements is the use of capillary electrophoresis (CE). With CE, one can employ immunosubtraction to select a region of interest in the β region thereby excluding much of the normal proteins from the M-protein measurement. Recent development of an immunochemical method distinguishing heavy/light chain pairs (separately measuring IgGK and IgGL, IgAK and IgAL, and IgMK and IgML) provides measurements that could exclude polyclonal contaminants of the same heavy chain with the uninvolved light chain type. Yet, even heavy/light results contain an immeasurable quantity of polyclonal heavy/light chains of the involved isotype. Finally, use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) looms on the horizon as a means to provide more consistent and sensitive measurements of M-proteins.

Utility of nine-color, 11-parameter flow cytometry for detection of plasma cell neoplasms: a comparison with bone marrow morphologic findings and concurrent M-protein studies in serum and urine

OBJECTIVES

Multiparameter flow cytometry (MFC) is a widely available laboratory platform for the evaluation of plasma cell (PC) neoplasms. We assess the performance of a nine-color MFC assay that uses stain-lyse-fix processing of bone marrow aspirates, minimal wash steps, and high acquisition rates with analysis of up to 1.8 × 10(6) cells.

METHODS

MFC results were compared with microscopic examinations, immunohistochemical studies, and serum/urine M-protein measurements from patients with documented or suspected PC neoplasms.

RESULTS

Sensitivity exceeded that of microscopic examinations, with or without immunohistochemistry. In patients with PC myeloma, clonal PC detection by MFC fell in concert with M-protein levels. However, in a subset of patients, MFC detected clonal PCs after serum/urine studies turned negative.

CONCLUSIONS

The nine-color analytic cocktail eliminates duplication of PC gating reagents required for evaluation of the same epitopes using a five- or six-color approach. Fewer analytic cocktails result in lower instrument acquisition times per case, a significant factor for the large data sets required for optimal residual disease assessment. Finally, concurrent analysis of nine epitopes and two light scatter parameters aids detection of residual disease, particularly when it is mixed with polyclonal PCs.

Replacing urine protein electrophoresis with serum free light chain analysis as a first-line test for detecting plasma cell disorders offers increased diagnostic accuracy and potential health benefit to patients

OBJECTIVES

To determine the most clinically effective diagnostic testing strategy for plasma cell disorders in the clinical laboratory.

METHODS

Serum and urine samples from 2,799 patients with suspected plasma cell dyscrasias were tested by alternative diagnostic testing strategies consisting of serum protein electrophoresis (SPE) with either urine protein electrophoresis (UPE) or serum free light chain (sFLC) analysis.

RESULTS

The combination of sFLC analysis and SPE had the greatest sensitivity (100%), detecting abnormalities in all 124 patients diagnosed with plasma cell disorders. Routine sFLC testing would have had much potential health benefit for two patients in the study population. First, a patient who had a markedly abnormal sFLC result was diagnosed with light chain deposition disease by renal biopsy, but no abnormality was detected by SPE or UPE. Second, a patient diagnosed with multiple plasmacytomas following biopsy of a lung tumor had a grossly abnormal sFLC result but an equivocal weak-positive SPE result, and no urine sample was received by the laboratory for the patient.

CONCLUSIONS

Our study suggests that the combination of SPE and sFLC analysis is the most clinically effective first-line diagnostic testing strategy for detecting plasma cell disorders in the clinical laboratory.

Serum free light chains in clinical laboratory diagnostics

Monoclonal free light chains (FLCs) are important disease biomarkers in patients with plasma cell-proliferative disorders. The increasing evidence for clonal diversity and evolution in multiple myeloma highlights the importance of laboratory algorithms that measure both intact immunoglobulins and monoclonal FLCs, at diagnosis and when monitoring response to treatment. A particular focus in the field has been on the utility of serum FLC (sFLC) assays to replace urine electrophoresis for monoclonal FLC measurement. Due to the limited sensitivity and practical constraints of urine analysis, a serum-based algorithm of SPE and sFLC has been adopted by many laboratories as a first line screen in patients with suspected monoclonal gammopathies. This review will discuss the data supporting the use of this simple serum-based algorithm at initial diagnosis, including its utility for the rapid identification of monoclonal FLC in the setting of unexplained acute kidney injury, and provide a comprehensive review of the diagnostic sensitivity of sFLC in patients with multiple myeloma, AL amyloidosis and light chain deposition disease.

Optimization of utilization of serum protein analysis: role of the electronic medical record in promoting consultation by pathology

Screening for monoclonal gammopathies is usually done by serum protein electrophoresis (SPEP) and serum free light chain tests. SPEP may be followed by immunofixation electrophoresis (IFE). IFE may be ordered by the treating physician or be at the discretion of the pathologist. We examined the appropriateness of IFE ordering by treating physicians and report on our findings, follow-up changes to the ordering process, and results of the change. We retrospectively analyzed the data from our laboratory from April 2009 through July 2012. In April 2009, 3 options for test ordering were available for the clinicians: SPEP with reflex IFE, SPEP only, and SPEP with IFE. This test ordering option was limited to SPEP with reflex IFE only in April 2010. We compared the rates of SPEP and IFE performed in the 2 periods (ie, April 2009 through April 2010 and May 2010 through July 2012). There was a substantial drop in the IFE/SPEP ratio from 0.47 to 0.21. Review of electronic medical records by the consultant pathologist was instrumental in improving the utilization and enhancing the value of pathology consultation. Possible impacts on laboratory costs, revenue, and overall health care are also presented.

Use of serum free light chain analysis and urine protein electrophoresis for detection of monoclonal gammopathies

BACKGROUND

Serum free light chain (FLC) analysis is used in the prognostic assessment and monitoring of patients with monoclonal gammopathies (MG). Its use in detection of MG is less widespread despite good sensitivity for diseases poorly detected by serum protein electrophoresis (SPE), e.g., FLC disease and AL amyloidosis. FLC analysis may facilitate earlier diagnosis in these diseases. However, if replacing urine protein electrophoresis (UPE) in an initial screening algorithm, this must be balanced against any loss of detection of Bence Jones proteinuria (BJP).

METHODS

We assessed the effect of replacing UPE with FLC. Sensitivity of FLC for BJP was assessed in 126 clinical cases where UPE and FLC analyses were performed. Impact on disease detection was assessed from 753 patient sera tested by SPE and FLC and 128 patients matched associated urine samples.

RESULTS

Sensitivity of FLC for BJP was 98%. Use of FLC in routine testing increased the number of MG detected by 7%.

CONCLUSIONS

Using FLC alongside or in place of UPE can give clinical benefit through earlier diagnosis and hence treatment earlier in the patients' disease.

[Value of serum free light chains assay in plasma cell disorders]

The identification and quantification of the monoclonal immunoglobulin in Plasma Cell Disorders (PCD) is based on electrophoresis, immunofixation (IFE) and on immunoglobulins nephelometric measurement. Even though the combination of these techniques is highly sensitive, there are two entities which pose a diagnostic challenge: Non-secretory Multiple Myeloma (MM) and Amyloidosis (AL) patients. Furthermore, when it comes to the results, these techniques have a degree of subjective interpretation and the IFE does not provide quantitative results. Within these limitations a new assay capable of quantifying free light chains (FLC) in serum has been developed. This is a great improvement in PCD and its major indication is the diagnosis and monitoring of patients with AL and non-secretory MM. In addition, its use has been recommended in the screening of all gammopathies; in the prognostic evaluation of MM and other PCD; and the definition of the stringent complete response for patients who achieve a complete remission (CR) with negative IFE and a normalized FLC ratio.

Recommendations for Use of Free Light Chain Assay in Monoclonal Gammopathies

The serum immunoglobulin free light chain assay measures levels of free κ and λ immunoglobulin light chains. There are three major indications for the free light chain assay in the evaluation and management of multiple myeloma and related plasma cell disorders. In the context of screening, the serum free light chain assay in combination with serum protein electrophoresis and immunofixation yields high sensitivity, and negates the need for 24-hour urine studies for diagnoses other than light chain amyloidosis. Second, the baseline free light chains measurement is of major prognostic value in virtually every plasma cell disorder. Third, the free light chain assay allows for quantitative monitoring of patients with oligosecretory plasma cell disorders, including AL, oligosecretory myeloma, and nearly twothirds of patients who had previously been deemed to have non-secretory myeloma. In AL patients, serial free light chains measurements outperform protein electrophoresis and immunofixation. In oligosecretory myeloma patients, although not formally validated, serial free light chains measurements reduce the need for frequent bone marrow biopsies. In contrast, there are no data to support using free light chain assay in place of 24-hour urine electrophoresis for monitoring or for serial measurements in plasma cell disorders with measurable disease by serum or urine electrophoresis.

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.

Screening panels for detection of monoclonal gammopathies

BACKGROUND

The repertoire of serologic tests for identifying a monoclonal gammopathy includes serum and urine protein electrophoresis (PEL), serum and urine immunofixation electrophoresis (IFE), and quantitative serum free light chain (FLC). Although there are several reports on the relative diagnostic contribution of these assays, none has looked at the tests singly and in combination for the various plasma cell proliferative disorders (PCPDs).

METHODS

Patients with a PCPD and all 5 assays performed within 30 days of diagnosis were included (n = 1877). The diagnoses were multiple myeloma (MM) (n = 467), smoldering multiple myeloma (SMM) (n = 191), monoclonal gammopathy of undetermined significance (MGUS) (n = 524), plasmacytoma (n = 29), extramedullary plasmacytoma (n = 10), Waldenström macroglobulinemia (WM) (n = 26), primary amyloidosis (AL) (n = 581), light chain deposition disease (LCDD) (n = 18), and POEMS syndrome (n = 31).

RESULTS

Of the 1877 patients, 26 were negative in all assays. Omitting urine from the panel lost an additional 23 patients (15 MGUS, 6 AL, 1 plasmacytoma, 1 LCDD), whereas the omission of FLC lost 30 patients (6 MM, 23 AL, and 1 LCDD). The omission of serum IFE as well as urine lost an additional 58 patients (44 MGUS, 7 POEMS, 5 AL, 1 SMM, and 1 plasmacytoma).

CONCLUSIONS

The major impact of using a simplified screening panel of serum PEL plus FLC rather than PEL, IFE, and FLC is an 8% reduction in sensitivity for MGUS, 23% for POEMS (7 patients), 4% for plasmacytoma (1 patient), 1% for AL, and 0.5% for SMM. There is no diminution in sensitivity for detecting MM, macroglobulinemia, and LCDD.

Are renal reference intervals required when screening for plasma cell disorders with serum free light chains and serum protein electrophoresis?

Renal impairment and polyclonal hypergammaglobulinemia may abnormally increase the serum free light chain (sFLC) ratio, giving false-positive results with current reference intervals. We measured sFLCs with concomitant serum protein electrophoresis (SPEP) and urine protein electrophoresis (UPEP) in 281 patients. Results were interpreted relative to renal function (serum creatinine concentrations) and polyclonal hypergammaglobulinemia. Overall, 78 plasma cell disorders (PCDs) were detected with the serum panel of SPEP/sFLC vs 76 with SPEP/UPEP. In 13 samples with negative SPEP/UPEP, mildly increased ratios up to 3.1 (normal, 0.26-1.65) were observed: 10 were associated with increased serum creatinine and 1 with polyclonal hypergammaglobulinemia; 2 were unassociated with either condition. In 2 samples, decreased kappa/lambda ratios were identified that were clinically significant despite normal SPEP/UPEP. Two monoclonal gammopathies were identified with UPEP and sFLC, but samples were normal with SPEP. Screening for PCDs with a serum panel consisting of SPEP and the sFLC assays is a highly sensitive approach that could eliminate the need for UPEP. A mildly increased kappa/lambda ratio up to 3.1 was observed with increased serum creatinine and/or polyclonal hypergammaglobulinemia that was consistent with pathophysiologic changes, and, therefore, renal reference intervals are recommended.

International Myeloma Working Group guidelines for serum-free light chain analysis in multiple myeloma and related disorders

The serum immunoglobulin-free light chain (FLC) assay measures levels of free kappa and lambda immunoglobulin light chains. There are three major indications for the FLC assay in the evaluation and management of multiple myeloma and related plasma cell disorders (PCD). In the context of screening, the serum FLC assay in combination with serum protein electrophoresis (PEL) and immunofixation yields high sensitivity, and negates the need for 24-h urine studies for diagnoses other than light chain amyloidosis (AL). Second, the baseline FLC measurement is of major prognostic value in virtually every PCD. Third, the FLC assay allows for quantitative monitoring of patients with oligosecretory PCD, including AL, oligosecretory myeloma and nearly two-thirds of patients who had previously been deemed to have non-secretory myeloma. In AL patients, serial FLC measurements outperform PEL and immunofixation. In oligosecretory myeloma patients, although not formally validated, serial FLC measurements reduce the need for frequent bone marrow biopsies. In contrast, there are no data to support using FLC assay in place of 24-h urine PEL for monitoring or for serial measurements in PCD with measurable disease by serum or urine PEL. This paper provides consensus guidelines for the use of this important assay, in the diagnosis and management of clonal PCD.

Serum free light chain measurement aids the diagnosis of myeloma in patients with severe renal failure

BACKGROUND

Monoclonal free light chains (FLCs) frequently cause rapidly progressive renal failure in patients with multiple myeloma. Immunoassays which provide quantitative measurement of FLCs in serum, have now been adopted into screening algorithms for multiple myeloma and other lymphoproliferative disorders. The assays indicate monoclonal FLC production by the presence of an abnormal kappa to lambda FLC ratio (reference range 0.26-1.65). Previous work, however, has demonstrated that in patients with renal failure the FLC ratio can be increased above normal with no other evidence of monoclonal proteins suggesting that in this population the range should be extended (reference range 0.37-3.1). This study evaluated the diagnostic sensitivity and specificity of the immunoassays in patients with severe renal failure.

METHODS

Sera from 142 patients with new dialysis-dependent renal failure were assessed by serum protein electrophoresis (SPE), FLC immunoassays and immunofixation electrophoresis. The sensitivity and specificity of the FLC ratio's published reference range was compared with the modified renal reference range for identifying patients with multiple myeloma; by receiver operating characteristic curve analysis.

RESULTS

Forty one patients had a clinical diagnosis of multiple myeloma; all of these patients had abnormal serum FLC ratios. The modified FLC ratio range increased the specificity of the assays (from 93% to 99%), with no loss of sensitivity. Monoclonal FLCs were identified in the urine from 23 of 24 patients assessed.

CONCLUSION

Measurement of serum FLC concentrations and calculation of the serum kappa/lambda ratio is a convenient, sensitive and specific method for identifying monoclonal FLC production in patients with multiple myeloma and acute renal failure. Rapid diagnosis in these patients will allow early initiation of disease specific treatment, such as chemotherapy plus or minus therapies for direct removal of FLCs.

Quantitation of serum free light chains in combination with protein electrophoresis and clinical information for diagnosing multiple myeloma in a general hospital population

BACKGROUND

Serum free light chain (SFLC) measurements have recently come into use as an aid for diagnosing monoclonal gammopathy. We evaluated SFLC measurements in combination with serum protein electrophoresis (SPE) and clinical information for diagnosing multiple myeloma (MM) in a hospital population.

METHODS

We measured SFLCs in 3818 sera received for SPE over a 1-year period when patient symptoms or biochemical findings suggested myeloma-related tissue damage (n = 1067). We reviewed SPE and SFLC results from 489 patients together with their final diagnoses obtained from the hospital information technology department.

RESULTS

SFLC measurement, combined with SPE and clinical information, allowed identification of 95% of patients (38 of 40) with previously undiagnosed MM, macroglobulinemia, or primary amyloidosis. Additionally, we identified 45 patients with monoclonal gammopathy of undetermined significance (MGUS) and 4 with plasmacytoma. Of patients followed at our hospital in whom SFLCs were not measured, only 1 patient was diagnosed with MM. This patient had anemia and was mistakenly not tested for SFLCs. An abnormal kappa/lambda ratio was found in 26 of 29 patients with MM but also in 36 of 203 patients with renal impairment, polyclonal immunoresponse, or other nonhematological diagnoses. None of the 203 patients with nonhematological disease had a kappa/lambda ratio <0.05 or >10.

CONCLUSIONS

The combined use of SPE, SFLC measurements, and clinical criteria allows MM to be efficiently diagnosed or excluded based on serum measurements only.

Diagnostic performance of serum free light chain measurement in patients suspected of a monoclonal B-cell disorder

The present study aimed to determine the diagnostic performance of different testing strategies to diagnose malignant B-cell disorder or monoclonal gammopathy of unknown significance (MGUS). Sensitivity and specificity were determined in 833 consecutive patients investigated for a monoclonal gammopathy. Serum protein electrophoresis (PE), serum kappa/lambda free light chain (FLC) ratio, and serum and urine immunofixation electrophoresis (IFE) were performed in all patients. Twenty-eight patients were diagnosed with a malignant plasma cell disorder, 25 with B-cell non-Hodgkin lymphoma and 156 with MGUS. Serum PE (with follow-up IFE) plus FLC had a sensitivity of 82.3% and a specificity of 96.8% and missed one plasmacytoma and 23 patients with MGUS. Serum IFE plus urine IFE had a sensitivity of 92.3% and a specificity of 100% and missed two MGUS patients. Serum IFE plus FLC had a sensitivity of 93.8% and a specificity of 96.8% and missed one MGUS patient. Serum PE plus FLC had a significantly lower sensitivity than serum IFE plus FLC or serum IFE plus urine IFE for the diagnosis of MGUS. The sensitivity of serum IFE plus FLC was comparable to the sensitivity of serum IFE plus urine IFE. The specificity of serum IFE plus FLC, however, was lower than the specificity of serum IFE plus urine IFE.

Value of serum free light chain testing for the diagnosis and monitoring of monoclonal gammopathies in hematology

The automated quantification of serum free kappa and lambda light chain concentrations provides a highly sensitive tool for the diagnosis and monitoring of monoclonal gammopathies. An abnormal kappa:lambda ratio supports the presence of clonal plasma cell expansion and requires further investigation. More than 94% of myeloma, light chain myeloma, and AL amyloidosis and, likewise, a majority of patients with light chain deposition disease are detectable with this technology. Importantly, these assays identify M-proteins in most patients with oligosecretory disease and permit their recruitment into clinical trials from which they have been previously excluded. Combining serum free light chain testing with traditional electrophoresis provides > 99% accuracy in the first-line diagnosis of monoclonal gammopathies and eliminates the need for urine testing in most instances. One third of patients with monoclonal gammopathy of undetermined significance have an abnormal free light chain ratio, and these patients harbor a greater risk of progression to plasma cell dyscrasia. For monitoring response to therapy, the international uniform response criteria define a normal free light chain ratio as an essential element of the "stringent complete response" category. Because the half-life of free light chains is < 6 hours, free light chain measurements at short sampling intervals allow real-time measurement of treatment-induced tumor kill, and provide prompt indications of chemosensitivity, dose adequacy, need for alternative approaches, and even prognosis, as demonstrated in AL amyloidosis if the involved free light chain concentration normalizes. Clinical applications of these assays will likely increase as their utility is more widely explored.

Elimination of the need for urine studies in the screening algorithm for monoclonal gammopathies by using serum immunofixation and free light chain assays

OBJECTIVE

To determine the relative diagnostic contribution of urine assays as part of the screening algorithm for monoclonal gammopathies.

PATIENTS AND METHODS

We identified 428 patients with a monoclonal gammopathy and monoclonal urinary protein at initial diagnosis of plasma cell dyscrasia who had also undergone serum immunofixation and serum free light chain quantitation within 30 days of diagnosis. The laboratory results for serum protein electrophoresis, serum immunofixation, serum free light chain, urine protein electrophoresis, and urine immunofixation were reviewed.

RESULTS

The patients had diagnoses of multiple myeloma, primary amyloid, monoclonal gammopathy of undetermined significance, smoldering multiple myeloma, solitary plasmacytomas, and other less frequently detected monoclonal gammopathies. All 428 had a monoclonal urine protein, 85.7% had an abnormal serum free light chain kappa/lambda ratio, 80.8% had an abnormal serum protein electrophoresis, and 93.5% had an abnormal serum immunofixation result. All 3 serum assays were normal in only 2 patients, 1 of whom had monoclonal gammopathy of undetermined significance (idiopathic Bence Jones proteinuria) and 1 whose urine sample contained an intact monoclonal immunoglobulin but whose serum and subsequent urine samples showed no evidence of a monoclonal gammopathy.

CONCLUSION

Discontinuation of urine studies and reliance on a diagnostic algorithm using only serum studies (protein electrophoresis, immunofixation, and free light chain quantitation) missed 2 (0.5%) of the 428 monoclonal gammopathies with urinary monoclonal proteins, and these 2 cases required no medical intervention.

Serum Free Light Chains: An Alternative to the Urine Bence Jones Proteins Screening Test for Monoclonal Gammopathies

Background: Retrospective analyses have established the role of quantitative serum free light chains (FLCs) in the diagnosis of monoclonal light chain disorders. The aims of this study were to assess (a) whether the addition of serum FLCs to serum protein electrophoresis (SPEP) identified additional patients with monoclonal gammopathies; (b) whether serum FLC measurements could replace urinalysis for Bence Jones protein (BJP); and (c) the cost/quality implications of routinely measuring serum FLCs.

Methods: Serum FLCs were added to consecutive requests for SPEP from August to November 2004 and measured by automated immunoassay.

Results: Seventy-one of 923 patients had abnormal serum FLC ratios. Seven patients with monoclonal gammopathies and 1 patient with malignant lymphoma (but no monoclonal band) were detected among 43 patients with negative SPEP but positive serum FLC ratios. Thirty-five patients with negative SPEP had false-positive serum FLC ratios. The false-positive rate for a ratio &gt;1.65 was higher than previously described and associated with polyclonal increases in immunoglobulins and renal impairment. Serum FLC ratios were normal in 2 of 13 patients with low-level persistent urine BJP. However, no significant pathology would have been missed by replacing BJP with serum FLCs. Revenue and manpower savings offset 60% of the costs of serum FLCs.

Conclusions: Additional diagnostic information is gained by adding serum FLCs to SPEP as first-line tests for investigating possible B-cell disorders. The quality of the diagnostic service is enhanced by more confident exclusion of light chain disorders and improved interpretive assessment of SPEP and immunofixation electrophoresis.

Nonsecretory plasma cell myeloma--becoming even more rare with serum free light-chain assay: a brief review

CONTEXT

Nonsecretory plasma cell myeloma is characterized by an absence of detectable monoclonal protein in both the serum and urine. It is generally reported to comprise approximately 1% to 5% of all cases of plasma cell myeloma and, because of its rarity, requires a high index of suspicion and bone marrow biopsy to establish the diagnosis.

OBJECTIVE

Review the diagnostic strategy when nonsecretory plasma cell myeloma is a clinical consideration in light of a relatively new serum free light chain assay.

DATA SOURCES

Case study and review of the literature.

CONCLUSIONS

Initial data using a recently developed nephelometric serum free light chain assay suggests that only about one fourth of nonsecretory plasma cell myeloma cases may be truly nonsecretory. The definition of nonsecretory plasma cell myeloma should be modified to exclude cases with evidence of clonality using the serum free light chain assay.