Comparison of Freelite™ and N Latex serum free light chain assays in subjects with end stage kidney disease on haemodialysis

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.

2024 Australia-New Zealand Expert Consensus Statement on Cardiac Amyloidosis

Over the past 5 years, early diagnosis of and new treatments for cardiac amyloidosis (CA) have emerged that hold promise for early intervention. These include non-invasive diagnostic tests and disease modifying therapies. Recently, CA has been one of the first types of cardiomyopathy to be treated with gene editing techniques. Although these therapies are not yet widely available to patients in Australia and New Zealand, this may change in the near future. Given the rapid pace with which this field is evolving, it is important to view these advances within the Australian and New Zealand context. This Consensus Statement aims to update the Australian and New Zealand general physician and cardiologist with regards to the diagnosis, investigations, and management of CA.

Assessment of current clinical practice throughout the UK for the diagnosis and management of monoclonal gammopathy of renal significance

Since the inception of the term monoclonal gammopathy of renal significance (MGRS) in 2012 by the International Kidney and Monoclonal Gammopathy Research Group, there have been no consensus guidelines specifically pertaining to the UK regarding to patient management. We aimed to identify both regional and cross-discipline variation in current clinical practice, to provide insight and rationale for a potential standardised pathway in the future. A national survey of 88 consultants from the disciplines of haematology and nephrology was conducted between June 2020 and July 2021. Agreement was evident for aspects of the diagnostic pathway, including presenting features likely to raise suspicion of MGRS and the most pertinent confounding factors to consider before renal biopsy. However, significant variability was identified in both the cohort of diagnostic tests used, as well as urinary work-up for patients with suspected MGRS. Treatment and monitoring frequency was also an aspect of management identified as variable. Despite differences in clinical practice across the UK, MGRS diagnosis was widely regarded to be the joint responsibility of both disciplines. The results provide an indication of inter-regional and interdisciplinary differences in practice, highlighting the need for improved awareness and standardised protocol for management of MGRS that applies to the UK population.

Expanded hemodialysis as effective alternative to on-line hemodiafiltration: A randomized mid-term clinical trial

Expanded hemodialysis (HDx), using medium cut-off membrane, is a novel therapy that effectively clears middle molecules (MMs). We aimed to compare HDx to hemodiafiltration (HDF) in an open randomized clinical study. Patients currently on HDF (age 18-80 years; on HDF >3 months) were randomized to switch to HDx (N = 21) or continue HDF (N = 22) with a 24-week follow-up. Pre- to post-dialysis reduction ratios (RR) and changes in pre-dialysis levels over time were evaluated for MMs and clinical biomarkers. Use of erythropoiesis-stimulating agents (ESAs) was assessed. HDx showed greater RR for YKL-40 while RR appeared similar between groups for beta₂ -microglobulin, FGF-23, and free light chains. Intradialytic changes in inflammatory biomarkers (IL-6, CRP, PTX3) did not differ between therapies. Changes from baseline to 12 and 24 weeks did not differ between groups for MMs, inflammatory markers, albumin, fibrinogen, hemoglobin, PTH, and phosphorus. Use of ESAs tended to decrease in HDx arm while remaining stable in HDF arm. HDx appeared safe with similar clinical effectiveness as HDF. With fewer requirements and resource needs, HDx provides an attractive alternative to HDF.

Serum and Urine Protein Electrophoresis and Serum-Free Light Chain Assays in the Diagnosis and Monitoring of Monoclonal Gammopathies

BACKGROUND

Laboratory methods for diagnosis and monitoring of monoclonal gammopathies have evolved to include serum and urine protein electrophoresis, immunofixation electrophoresis, capillary zone electrophoresis, and immunosubtraction, serum-free light chain assay, mass spectrometry, and newly described QUIET.

CONTENT

This review presents a critical appraisal of the test methods and reporting practices for the findings generated by the tests for monoclonal gammopathies. Recommendations for desirable practices to optimize test selection and provide value-added reports are presented. The shortcomings of the serum-free light chain assay are highlighted, and new assays for measuring monoclonal serum free light chains are addressed.

SUMMARY

The various assays for screening, diagnosis, and monitoring of monoclonal gammopathies should be used in an algorithmic approach to avoid unnecessary testing. Reporting of the test results should be tailored to the clinical context of each individual patient to add value. Caution is urged in the interpretation of results of serum-free light chain assay, kappa/lambda ratio, and myeloma defining conditions. The distortions in serum-free light chain assay and development of oligoclonal bands in patients' status post hematopoietic stem cell transplants is emphasized and the need to note the location of original monoclonal Ig is stressed. The need for developing criteria that consider the differences in the biology of kappa and lambda light chain associated lesions is stressed. A new method of measuring monoclonal serum-free light chains is introduced. Reference is also made to a newly defined entity of light chain predominant intact immunoglobulin monoclonal gammopathy. The utility of urine testing in the diagnosis and monitoring of light chain only lesions is emphasized.

A study from The Mayo Clinic evaluated long-term outcomes of kidney transplantation in patients with immunoglobulin light chain amyloidosis

Longer survival using modern therapies has increased the number of patients with immunoglobulin light-chain amyloidosis receiving kidney transplantation. We evaluated 60 patients with immunoglobulin light chain amyloidosis who underwent kidney transplantation based on their hematologic response for outcomes of death, graft failure, and complications. Patient hematologic responses (light-chain in blood or urine) prior to kidney transplantation were three patients had no response, five had a partial response, six had a very good partial response, 37 had a complete response, and nine were treatment-naive patients (never treated for this disorder). After transplantation, seven of nine treatment-naive patients achieved a complete response. The median follow-up for the entire transplant cohort was 61 months. The estimated median overall survival from the time of kidney transplantation was 123 months for the entire group. Median overall survival was not reached for the very good partial response plus complete response groups, it was 47 months for no response plus partial response groups, and 117 months for the treatment-naive group (all significantly different). Median overall survival of very good partial response was 81 months, while the median was not reached in the complete response group (no significant difference). The time to amyloid recurrence was significantly longer in complete response compared to very good partial response (median 181 vs 81 months). Death-censored graft survival at one- and five-years was 98.3%, and 95.8%, respectively for all groups. Of the 60 patients, three had allograft failure, 19 died with a functioning graft, and 13 had an amyloid recurrence. Thus, outcomes after kidney transplant in patients with immunoglobulin light-chain amyloidosis seem acceptable if a very good partial response or complete response is achieved either before or after transplantation.

Comparison of 2 Serum-Free Light-Chain Assays in CKD Patients

Introduction

Quantification of serum-free light chains (FLCs) is important in the diagnosis and monitoring of paraprotein-related diseases. There are currently 2 FLC assays available: the Freelite assay (Binding Site) and the N Latex assay (Siemens). There is emerging evidence that these assays give different results, but it is not established how kidney dysfunction affects these assays differently.

Methods

In this study, we measured and compared serum FLCs in patients with mild-to-moderate chronic kidney disease (CKD) using both assays.

Results

Although κ FLCs are higher by Freelite, λ FLCs are higher by N Latex. Both κ and λ FLCs correlate inversely with estimated glomerular filtration rate (eGFR) in the 2 assays, but this effect is more pronounced in λ-free light-chain measurement by N Latex. Consequently, although the κ/λ ratio by Freelite is inversely correlated by eGFR, the κ/λ ratio by N Latex is positively correlated with eGFR.

Conclusion

Our results clearly demonstrate that the 2 available FLC assays cannot be used interchangeably in patients with CKD.

The evaluation of monoclonal gammopathy of renal significance: a consensus report of the International Kidney and Monoclonal Gammopathy Research Group

The term monoclonal gammopathy of renal significance (MGRS) was introduced by the International Kidney and Monoclonal Gammopathy Research Group (IKMG) in 2012. The IKMG met in April 2017 to refine the definition of MGRS and to update the diagnostic criteria for MGRS-related diseases. Accordingly, in this Expert Consensus Document, the IKMG redefines MGRS as a clonal proliferative disorder that produces a nephrotoxic monoclonal immunoglobulin and does not meet previously defined haematological criteria for treatment of a specific malignancy. The diagnosis of MGRS-related disease is established by kidney biopsy and immunofluorescence studies to identify the monotypic immunoglobulin deposits (although these deposits are minimal in patients with either C3 glomerulopathy or thrombotic microangiopathy). Accordingly, the IKMG recommends a kidney biopsy in patients suspected of having MGRS to maximize the chance of correct diagnosis. Serum and urine protein electrophoresis and immunofixation, as well as analyses of serum free light chains, should also be performed to identify the monoclonal immunoglobulin, which helps to establish the diagnosis of MGRS and might also be useful for assessing responses to treatment. Finally, bone marrow aspiration and biopsy should be conducted to identify the lymphoproliferative clone. Flow cytometry can be helpful in identifying small clones. Additional genetic tests and fluorescent in situ hybridization studies are helpful for clonal identification and for generating treatment recommendations. Treatment of MGRS was not addressed at the 2017 IKMG meeting; consequently, this Expert Consensus Document does not include any recommendations for the treatment of patients with MGRS.

This Expert Consensus Document from the International Kidney and Monoclonal Gammopathy Research Group includes an updated definition of monoclonal gammopathy of renal significance (MGRS) and recommendations for the use of kidney biopsy and other modalities for evaluating suspected MGRS

Inter-assay variability in automated serum free light chain assays and their use in the clinical laboratory

Serum κ and λ free light chain levels are markers of plasma cell proliferation, and their measurements have been included in recent guidelines by the International Myeloma Working Group for the management of patients with plasma cellular dyscrasias. Five in vitro diagnostic methods for the immunochemical quantification of serum free light chains (FLC) are available, three based on polyclonal antibodies (Freelite^®, The Binding Site; FLC ELISA κ and λ, Sebia; human κ and λ FLC, Diazyme Laboratories) and two on monoclonal antibodies (N Latex FLC, Siemens Healthineers; Seralite^®, Sebia). Several studies have shown that these methods cannot be used interchangeably for the follow-up of patients because measured κ and λ FLC concentrations may differ significantly, especially at high levels. Because no international reference material for the measurement of FLC is available, it is not possible to establish which method is the most accurate. For this reason, knowledge about the analytical and diagnostic performances of the assays used is important. The aim of this review is to describe the main analytical features of the κ and λ FLC assays and how they may influence the clinical use of these parameters.

Serum free light chain quantitative assays: Dilemma of a biomarker

BACKGROUND

Serum free light chains detection assays are consistently meeting greater interest for the diagnosis and monitoring of monoclonal gammopathies and plasma cell dyscrasias. Nowadays, there are neither standardized methods nor reference material for the determination of free light chains; for this reason, it is important to compare two different assays used in clinical laboratory.

METHODS

We evaluated 300 serum samples from patients with B-cell disorders and compared the analytical performances of both assay. Each test was assayed on both testing platforms (Siemens Dade Behring BN II Nephelometer and SPAPLUS by The Binding Site). κ/λ ratios were determined and compared. Results were analyzed by Passing-Bablok and Bland-Altman plots to evaluate comparability of the two techniques and to determine bias.

RESULTS

The reproducibility of both assays is acceptable, reaching minimum and desirable analytical goals derived from biological variability. However, values are not interchangeable between systems. This study shows that the two systems do not allow results to be transferred from one method to the other even if they display good agreement.

CONCLUSION

Our study highlights the importance of elaborating an international standard for free light chains quantification in order to offer homogeneous results as well as guarantee harmonization of values among laboratories. Moreover, the assays should be validated in specific patient groups to determine that they are clinically fit for purpose.

Evaluation of the Impact of Renal Failure on Correlation and Concordance Between 2 Free Light Chain Assays

BACKGROUND

Free light chain (FLC) assays are essential for diagnosis and follow-up of plasma cell dyscrasia. Two assays are available: Freelite (Binding Site) and N Latex FLC (Siemens). The aim of our study was to evaluate the impact of renal failure on concordance and correlation between the 2 FLC assays.

METHODS

FLC measurements using both assays were performed on 1215 fresh serum samples from patients with or without monoclonal gammopathy and renal failure. Concordance and correlation were evaluated using Passing-Bablock regression, Pearson correlation coefficient, and the Cohen kappa coefficient, taking into account the renal failure stage (evaluated with Chronic Kidney Disease-Epidemiology Collaboration formulae) and evaluation of treatment response in patients' follow-up.

RESULTS

A good correlation was demonstrated between both assays, irrespective of the renal failure stage (Pearson correlation coefficient > 0.90). For FLC ratio interpretation, there remained 7.6% to 20.8% discordances between the 2 methods throughout the whole range of renal impairment. To evaluate FLC evolution in patient follow-up, 41 patients were selected with at least 6 consecutive serum samples being collected during the study period: we observed a concordant evolution of FLC concentrations between both assays. However, few discrepancies were observed with 4 patients.

CONCLUSIONS

Despite adjusted reference ranges for Freelite FLC ratio, there are approximately 12.5% discrepancies in interpretation of FLC ratio between the 2 available assays. They are not linked to renal failure stage and neither of the assays performed better than the other: results must be interpreted taking into account clinical data and the same assay must be used for patient follow-up.