Serum Free Light Chain Assay: Shift Toward a Higher κ/λ Ratio

Comparison of 2 Free Light Chain Assays: Performance of the Free Light Chain Ratio as a Risk Factor for MGUS Progression

BACKGROUND

New immunoglobulin free light chain (FLC) assays are available. Despite analytical differences, it seems possible to use free light chain ratios (FLCr) generated by different assays and apply similar cut-points for the diagnosis of multiple myeloma. It is still unknown if we can use different assays for risk stratification of patients with monoclonal gammopathy of undetermined significance (MGUS).

METHODS

Patients diagnosed with MGUS (N = 923) had FLC tested using a nephelometric FreeLite (Binding Site) assay on BNII instruments (Siemens) and a Sebia FLC assay (Sebia) on a DS2 ELISA analyzer (Dynex). Patients were followed up for progression to any plasma cell dyscrasia (PCD) for several decades. The Mayo MGUS risk stratification model for progression was assessed with both assays (M-spike >1.5 g/dL; non-IgG isotype and abnormal FLCr), using package insert reference intervals (RI) and a new metric called principal component 2 (PC2).

RESULTS

There were 94 events of progression to PCD in the cohort during a median of 38 years of follow-up. Freelite and Sebia FLC showed similar hazard ratios in the risk models for elevated FLCr. An alternative clinical decision point lower than the package insert RI was evaluated for the Sebia assay, which improved risk stratification for patients with a low FLCr. The PC2 metric showed similar performance to the FLCr in models, without superior benefit.

CONCLUSIONS

The Sebia ELISA-based FLC assay can be employed in an MGUS risk stratification model with similar performance to the original 2005 risk stratification model using the FreeLite assay.

Comparison of 2 Serum Free Light Chain Assays with Creatinine Normal and Abnormal Populations Demonstrates the Need for Standardization

BACKGROUND

The objective of this study was to compare The Binding Site's Freelite on Optilite and Diazyme's Kappa/Lambda free light chains (K/L FLC) on Abbott Architect c8000 with healthy and renal insufficient populations and to evaluate their respective reference intervals for serum free light chains (sFLCs).

METHODS

Two hundred sixty serum samples were measured for creatinine and sFLCs by both assays and a subset by immunofixation electrophoresis. Verification of manufacturer-defined reference intervals was assessed.

RESULTS

Kappa free light chains (KFLC) showed excellent correlation of 0.998 R2 with a slope of 0.73. For Lambda free light chains (LFLC), an acceptable correlation of 0.953 R2 was found with a slope of 1.50 as well as a skewness-based difference with a -12.70 intercept. Healthy estimated glomerular filtration rate (eGFR) ≥60 reference interval verification of central 95% could not be confirmed for either Freelite or Diazyme although LFLC was much closer than KFLC for both assays with Freelite KFLC recovering only 37% of values within reference interval claims. The K/L FLC ratio did not meet 100% claim for both Freelite (91%) and Diazyme (95%) among those with eGFR ≥60. Samples with eGFR ≤59 had increasingly higher levels of KFLC and LFLC for both assays. When comparing worsening eGFR status, Freelite recovered increasingly higher ratios while Diazyme recovered increasingly lower ratios.

CONCLUSIONS

Healthy reference intervals could not be verified for either Freelite or Diazyme. Renal reference intervals for Freelite are currently warranted while they are not recommended for Diazyme. The differences between these 2 assays can be minimized by standardization efforts such as recalibration.

Clinical specificity of two assays for immunoglobulin kappa and lambda free light chains

OBJECTIVES

Free light chain (FLC) assays and the ratio of κ/λ are recommended for diagnosis, prognosis and monitoring of plasma cell dyscrasias (PCD). Limited data exists on FLC clinical specificity in patients diagnosed with other conditions.

METHODS

We assessed the κ, λ, and κ/λ FLC ratio using the FreeLite assay and the Sebia FLC ELISA assay in 176 patients with clinical presentations of fatigue, anemia, polyclonal hypergammaglobulinemia, joint disorders, kidney disease and non PCD-cancers with no monoclonal protein observed on serum protein electrophoresis or MASS-FIX immunoglobulin isotyping. Manufacturer defined reference intervals (RI) and glomerular filtration rate (GFR) specific RI (renal RI) were utilized.

RESULTS

For the κ/λ ratio, 68.7 % (121/176) of specimens on the FreeLite and 87.5 % (154/176) of specimens on the Sebia assay were within RI. For κ, 68.2 % (120/176) and 72.2 % (127/176) of results were outside RI for FreeLite and Sebia respectively. For λ, 37.5 % (66/176) and 84.1 % (148/176) of FreeLite and Sebia results were outside RI. With FreeLite and Sebia, patients with kidney disease (n=25) had the highest κ/λ ratios. 44 patients (25.0 %) had GFR <60 mL/min/BSA. When renal RI were applied, 13.6 % had a FLCr outside the renal RI with FreeLite, and 4.5 % with Sebia.

CONCLUSIONS

In a cohort of patients with signs and symptoms suggestive of PCDs, but ultimately diagnosed with other conditions, Sebia FLC had improved clinical specificity relative to FreeLite, if one was using an abnormal κ/λ ratio as a surrogate for monoclonality.

Establishment of reference intervals for free light chains and immunoglobulins in Saudi population

OBJECTIVES

Testing of serum-free light chains kappa (κ) and lambda (λ), along with ratio (FLCR) is essential for the diagnosis and management of monoclonal gammopathies. Accurate clinical diagnosis depends upon appropriate local population reference intervals (RIs). This study examined the Saudi population for serum-free light chains and other immunoglobulins to establish RIs and to explore variations in the test results by using the International Federation for Clinical Chemistry and Laboratory Medicine's global protocol for harmonized implementation of RI study.

METHODS

A total of 180 healthy Saudi adults were recruited. All serum samples were assayed using the Freelite reagents from the Binding Site. The variation in reference values attributable to sex, age, BMI, and region was calculated by ANOVA as a standard deviation ratio (SDR). The RIs for the FLCR were derived by the parametric method and validated by using samples from patients with hypo- and hypergammaglobulinemia.

RESULTS

The new RIs for free κ and FLCR were shifted to a higher side from the manufacturer-adapted RIs. Based on the SDR cutoff value (>0.4), between-sex partition RIs were not required for all analytes except IgM. Validation using patients with hypo- or hypergammaglobulinemia and without multiple myeloma, was all within the new RI. BMI, smoking, and exercise were not relevant sources of variation for any analyte.

CONCLUSIONS

Locally derived RIs for free light chains and immunoglobulins analytes specific for Saudis were established after careful consideration of various factors. These RIs were more reliable than those provided as guidance by the manufacturer, or from other countries, for appropriate classification and prediction of disease progression for Saudi patients.

Kappa Free Light Chain Drift Prompts the Need for a New Upper Limit of Normal Free Light Chain Ratio to Avoid an Epidemic of Kappa Light Chain Monoclonal Gammopathy of Undermined Significance

BACKGROUND

Multiple laboratory tests are employed for detection of monoclonal proteins in patients and include serum protein electrophoresis (SPEP), immunofixation electrophoresis, free light chain (FLC) immunoassay, and mass spectrometry (Mass-Fix). Recently, reports on a drift in FLC quantitation results have been brought to light.

METHODS

We studied a cohort of 16 887 patients whose sera were tested for a monoclonal protein by a FLC assay, serum protein electrophoresis, and Mass-Fix. This is a retrospective study designed to assess the impact of a drift on the performance of FLC ratio (rFLC) in groups of patients with and without detectable plasma cell disorders (PCDs).

RESULTS

The results demonstrated that 63% of patients with monoclonal protein equal or higher than 2 g/L (by SPEP) had an abnormal rFLC (reference range 0.26-1.65). Conversely, 16% of patients with undetectable monoclonal protein by other methods (i.e., SPEP and Mass-Fix) who also had no record of treated PCD had an abnormal rFLC. In these cases, there was an imbalance in the number of kappa high rFLCs to lambda low rFLCs of 201 to 1.

CONCLUSIONS

The results of this study suggest decreased specificity of rFLC for a monoclonal kappa FLC in the 1.65 to 3.0 range.

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.

Monoclonal gammopathy of renal significance: Multidisciplinary approach to diagnosis and treatment

Monoclonal gammopathy of renal significance (MGRS) is a hemato-nephrological term referring to a heterogeneous group of kidney disorders characterized by direct or indirect kidney injury caused by a monoclonal immunoglobulin (MIg) produced by a B cell or plasma cell clone that does not meet current hematologic criteria for therapy. MGRS-associated kidney diseases are diverse and can result in the development of end stage kidney disease (ESKD). The diagnosis is typically made by nephrologists through a kidney biopsy. Many distinct pathologies have been identified and they are classified based on the site or composition of the deposited Mig, or according to histological and ultrastructural findings. Therapy is directed towards the identified underlying clonal population and treatment decisions should be coordinated between hematologists and nephrologists in a multidisciplinary fashion, depend on the type of MGRS, the degree of kidney function impairment and the risk of progression to ESKD.

Serum Free Light Chain Quantification Testing: Comparison of Two Methods for Disease Monitoring

Background

Levels of free immunoglobulin light chains in serum and urine are a sensitive measure of dysregulated immunoglobulin synthesis. The development of an assay for free light chains in serum was a major advance in laboratory testing for monoclonal gammopathies. The original assay by The Binding Site, called Freelite®, has been in common use in laboratory monitoring of monoclonal gammopathies. Two clinical entities, myeloma-defining condition and light chain-predominant multiple myeloma, rely on quantitative measurements of serum free light chains.

Methods

Using polyclonal antisera specific to free light chains, Diazyme Laboratories developed a latex immunoturbidimetric assay for quantification of human kappa and lambda serum free light chains. We evaluated the Diazyme assay by comparing the results of kappa and lambda free light chain quantification, and kappa/lambda ratio with the results on the same specimens by the Freelite method. We also compared the correlation of the 2 methods to evaluate response to treatment and to changes in clinical status of patients with multiple myeloma.

Results

The results of Freelite and Diazyme methods are comparable. There was no statistically significant difference in the performance of the 2 assays for quantification of light chains, kappa/lambda ratio, or correlation of clinical parameters from patients with multiple myeloma at various stages of monitoring the disease in 2 geographically diverse laboratory and clinical environments.

Conclusions

The Diazyme method is comparable to Freelite and provides an opportunity to add the test to front-end automation and improvement in efficiency of the assay.

Using Two Detection Methods to Observe the Changes and Significance of Free Light Chain in Serum and Urine in Patients with Renal Insufficiency

Background

Free light chains κ and λ (FLC κ, FLC λ) are of great significance in diagnostic and monitoring monoclonal gammopathy. Freelite and N-Latex methods are two common monitoring methods at present. But the two meanings are not completely equivalent, especially for patients with renal insufficiency. We analyzed the changes of serum and urine FLC in renal insufficiency patients without monoclonal gammopathy and the clinical significance of these changes.

Methods

This study is an observational study. Patients ≥ 18 years old, who met the diagnostic criteria of chronic kidney disease (CKD), excluding monoclonal gammopathy, were selected. Fasting serum and 24-hour urine were taken to detect serum FLC κ, serum FLC λ, SCr, serum β₂-microglobulin, urinary FLC κ, urinary FLC λ, urinary α₁-microglobulin, and urinary β₂-microglobulin.

Results

There was a good correlation between the two methods for determining serum/urinary FLC. No matter serum or urine, FLC showed a good correlation with renal function by the N-Latex method, but not by the Freelite method. Under the N-Latex method, FLC κ/λ remained stable, which was basically within the reference range of healthy people and was not affected by renal function. There was a good correlation between FLC detected by N-Latex and microglobulin in serum and urine.

Conclusion

When the concentration of FLC is low, the N-Latex method is more recommended to monitor FLC. The FLC measured by the N-Latex method is more closely related to renal function. The ratio of FLC κ/λ determined by the N-Latex method remained stable within the recommended range.

Alteration of the Gut Microbiome in Chronic Kidney Disease Patients and Its Association With Serum Free Immunoglobulin Light Chains

Objectives

Gut dysbiosis is associated with chronic kidney disease (CKD), and serum free immunoglobulin light chains (FLCs) are biomarkers for CKD. This study aims to assess the CKD gut microbiome and to determine its impact on serum FLC levels.

Methods

To control for confounders, 100 patients and sex- and age-matched healthy controls (HCs) were recruited. The gut microbiome was assessed by sequencing 16S rRNA gene V3-V4 hypervariable regions. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States was applied to infer functional metabolic pathways. When observing group differences in the microbiome and predicted metabolic pathways, demographic confounders were adjusted using binary logistic regression; when examining impacts of the gut microbiome and metabolic pathways on serum FLCs, factors influencing FLC levels were adjusted using multiple regression.

Results

Principal coordinate analysis revealed a significantly different bacterial community between the CKD and HC groups (P < 0.05). After adjusting for confounders, lower Chao 1, observed species and Shannon indices based on binary logistic regression predicted CKD prevalence. Actinobacteria, Alistipes, Bifidobacterium and Bifidobacterium longum enrichment, upregulation of metabolic pathways of bacterial toxin, chloroalkane and chloroalkene degradation, and Staphylococcus aureus infection also predicted CKD prevalence (P < 0.05). Furthermore, depletion of Actinobacteria and Bifidobacterium and reduced chloroalkane and chloroalkene degradation predicted high levels of FLC λ (P < 0.05).

Conclusions

Gut dysbiosis in CKD patients was confirmed by controlling for confounders in the present study. Additionally, the association between gut dysbiosis and FLC λ levels demonstrates the existence of crosstalk between the microbiome and immune response in CKD.

MASS-FIX for the detection of monoclonal proteins and light chain N-glycosylation in routine clinical practice: a cross-sectional study of 6315 patients

Immunoenrichment-based matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), termed MASS-FIX, offers several advantages over immunofixation for the detection and isotyping of serum monoclonal protein, including superior sensitivity and specificity, the ability to differentiate therapeutic monoclonal antibodies, and the rapid identification of light chain (LC) N-glycosylation. We identified 6315 patients with MASS-FIX performed at our institution since 2018. Of these, 4118 patients (65%) with a wide array of plasma cell disorders (PCD), including rare monoclonal gammopathies of clinical significance, had a positive MASS-FIX. Two-hundred twenty-one (5%) of the MASS-FIX positive patients had evidence of LC N-glycosylation, which was more commonly identified in IgM heavy chain isotype, kappa LC isotype, and in diagnoses of immunoglobulin light chain (AL) amyloidosis and cold agglutinin disease (CAD) compared to other PCD. This cross-sectional study describes the largest cohort of patients to undergo MASS-FIX in routine clinical practice. Our findings demonstrate the widespread utility of this assay, and confirm that LC N-glycosylation should prompt suspicion for AL amyloidosis and CAD in the appropriate clinical context.

Serum free light chain reference intervals in an Optilite and their influence on clinical guidelines

BACKGROUND

Serum free light chain (FLC) analysis has been incorporated into the International Myeloma Working Group guidelines for the diagnosis and management of all monoclonal gammopathies. These recommendations were solely based on a single assay method (Freelite assay) and instrument. Here, we establish new reference intervals (RIs) for kappa and lambda FLC and the kappa-lambda difference and sum and a new diagnostic range for kappa/lambda FLC ratio (K/L-FLC) in an Optilite turbidimeter (The Binding Site) with the Freelite assay.

METHODS

To establish new RIs, the CLSI EP28-A3C protocol was applied to 249 sample blood donors from Fuenlabrada, Spain, and the central 95% and total range were estimated. Samples from patients with polyclonal hypo- and hypergammaglobulinemia were used for the evaluation of K/L-FLC as a monoclonal proliferation index.

RESULTS

The new RIs and the new K/L-FLC diagnostic range for the Optilite (0.65-2.56 mg/L) are very different from those in on the guidelines (0.26-1.65 mg/L). We propose new RIs for the K - L difference and the K + L sum. Diagnostic range validation as a monoclonal proliferation index with samples with hypo- and hypergammaglobulinemia confirms this new range.

CONCLUSIONS

In this study, we present the FLC RI for Freelite reagents measured on an Optilite turbidimeter. These ranges are different from those provided by the manufacturer and from those used in most studies in the literature, which may lead to patient misclassification. Manufacturers and clinical laboratories must strive to provide RIs for the technology they are using and for their population.