External quality assessment of M-protein diagnostics: a realistic impression of the accuracy and precision of M-protein quantification

Improving Interpretation Consistency of Serum Capillary Electrophoresis by Development of Quantitative Graphic Indexes

Capillary zone electrophoresis-immunosubtraction (CZE-IS) is an essential laboratory test in diagnosing plasma cell neoplasms. However, the current interpretation of the test results is subjective. To evaluate CZE-IS in a more precise manner, this study proposed five key indexes, namely sharpness index, light chain index, immunoglobulin G index, immunoglobulin A index, and immunoglobulin M index. The reference intervals of these indexes were established using CZE-IS curve data from a clinical laboratory of a referral medical center. A total of 1000 cases with normal electrophoretic patterns were sampled for reference intervals establishment, and an additional 20 cases were included for validation. The following reference intervals in the γ zone were established: 1-6 (sharpness index), 1.06-2.71 (light chain index), 37-454 (immunoglobulin G index), (-9)-41 (immunoglobulin A index), and (-16)-46 (immunoglobulin M index). For the β2 zone, the reference intervals were 3-17 (sharpness index), 0.44-1.90 (light chain index), (-7)-61 (immunoglobulin G index), 2-117 (immunoglobulin A index), and (-12)-35 (immunoglobulin M index). The diagnostic performance of reference intervals of the proposed indexes in validation ranged from 95% to 100%. CZE-IS indexes provide the objective quantification of key characteristics of CZE-IS curves and improve the precision of CZE-IS interpretation.

A review of clinical guidelines, laboratory recommendations and external quality assurance programs for monoclonal gammopathy testing

Monoclonal gammopathy (MG) is a spectrum of diseases ranging from the benign asymptomatic monoclonal gammopathy of undetermined significance to the malignant multiple myeloma. Clinical guidelines and laboratory recommendations have been developed to inform best practices in the diagnosis, monitoring, and management of MG. In this review, the pathophysiology, relevant laboratory testing recommended in clinical practice guidelines and laboratory recommendations related to MG testing and reporting are examined. The clinical guidelines recommend serum protein electrophoresis, serum immunofixation and serum free light chain measurement as initial screening. The laboratory recommendations omit serum immunofixation as it offers limited additional diagnostic value. The laboratory recommendations offer guidance on reporting findings beyond monoclonal protein, which was not required by the clinical guidelines. The clinical guidelines suggested monitoring total IgA concentration by turbidimetry or nephelometry method if the monoclonal protein migrates in the non-gamma region, whereas the laboratory recommendations make allowance for involved IgM and IgG. Additionally, several external quality assurance programs for MG protein electrophoresis and free light chain testing are also appraised. The external quality assurance programs show varied assessment criteria for protein electrophoresis reporting and unit of measurement. There is also significant disparity in reported monoclonal protein concentrations with wide inter-method analytical variation noted for both monoclonal protein quantification and serum free light chain measurement, however this variation appears smaller when the same method was used. Greater harmonization among laboratory recommendations and reporting format may improve clinical interpretation of MG testing.

M-protein diagnostics in multiple myeloma patients using ultra-sensitive targeted mass spectrometry and an off-the-shelf calibrator

OBJECTIVES

Minimal residual disease status in multiple myeloma is an important prognostic biomarker. Recently, personalized blood-based targeted mass spectrometry (MS-MRD) was shown to provide a sensitive and minimally invasive alternative to measure minimal residual disease. However, quantification of MS-MRD requires a unique calibrator for each patient. The use of patient-specific stable isotope labelled (SIL) peptides is relatively costly and time-consuming, thus hindering clinical implementation. Here, we introduce a simplification of MS-MRD by using an off-the-shelf calibrator.

METHODS

SILuMAB-based MS-MRD was performed by spiking a monoclonal stable isotope labeled IgG, SILuMAB-K1, in the patient serum. The abundance of both M-protein-specific peptides and SILuMAB-specific peptides were monitored by mass spectrometry. The relative ratio between M-protein peptides and SILuMAB peptides allowed for M-protein quantification. We assessed linearity, sensitivity and reproducibility of SILuMAB-based MS-MRD in longitudinally collected sera from the IFM-2009 clinical trial.

RESULTS

A linear dynamic range was achieved of over 5 log scales, allowing for M-protein quantification down to 0.001 g/L. The inter-assay CV of SILuMAB-based MS-MRD was on average 11 %. Excellent concordance between SIL- and SILuMAB-based MS-MRD was shown (R2>0.985). Additionally, signal intensity of spiked SILuMAB can be used for quality control purpose to assess system performance and incomplete SILuMAB digestion can be used as quality control for sample preparation.

CONCLUSIONS

Compared to SIL peptides, SILuMAB-based MS-MRD improves the reproducibility, turn-around-times and cost-efficacy of MS-MRD without diminishing its sensitivity and specificity. Furthermore, SILuMAB can be used as a MS-MRD quality control tool to monitor sample preparation efficacy and assay performance.

A novel approach for more precise quantification of M-protein using variables derived from immunosubtraction electropherogram and associated biochemistry analytes

Introduction

Due to limitations in currently used methodologies, the widely acknowledged approach for quantifying M-protein (MP) is not available. If employed as a source of quantitative data, the immunosubtraction electropherogram (IS-EPG), a qualitative analysis of MP, has the potential to overcome known analytical issues. The aim of this study is to explore measured and derived variables obtained from immunosubtraction electropherogram as a tool for quantifying MP and to compare the derived results to currently available methods.

Materials and methods

Measurands were amplitudes of MP and albumin fractions. Assessed derived variables included also immunoglobulin (Ig) G, IgA, IgM and total protein data. Capillary electrophoresis was used for determination of MP (in % of total protein concentration, or concentration of MP in g/L) by perpendicular drop and tangent skimming method.

Results

Passing-Bablok analysis showed the most comparable results in D1Ig and D1nIg variables, and the largest discrepancies in AD1nIg and AD2nIg variables. The background presence had greater impact on D1nIg comparison results than did on D1Ig results. The contribution of albumin fraction data did not improve the comparability of the results. The coefficients of variation of derived variables were lower (maximum 3.1%) than those obtained by densitometric measurements, regardless of MP concentration, polyclonal background, or migration pattern (2.3-37.7%).

Conclusion

The amplitude of MP spike in IS-EPG is an valuable measurand to compute derived variables for quantifying MP. The most comparable results were achieved with the D1Ig variable. Patients with monoclonal gammopathy can benefit from increased precision employing an objective and background independent measurand, especially during longitudinal follow-up.

Applied capillary electrophoresis system affects screening for monoclonal gammopathy in serum: verification study of two eight-capillary systems

Capillary electrophoresis is a method with a long history of developments which enables monitoring of several pathological processes and has an irreplaceable role in screening for presence of M-protein. The aim of this study was to assess analytical performance of Sebia and Helena systems, as well as their screening efficiency for M-protein by identifying characteristic electrophoretic pattern abnormalities. The controls were analyzed in triplicate over a five-day period. Comparability testing was performed on 46 (Capillarys3Octa) and 49 (V8Nexus) serum samples with routinely used Capillarys2. Electropherograms (EPGs) were reviewed by two specialists independently to select samples for further processing by immunofixation. All precision test results met the eligibility criteria by Ricos et al. The correlation coefficients higher than 0.8 indicated excellent comparability although the results were slightly more comparable among the same manufacturer systems. There were no variations in observed abnormalities in EPGs when Capillarys systems were compared, but a disparity was detected in 11/49 EPGs on comparing Capillarys2 and V8Nexus. The cause of the detected difference could be in a different graphical presentation of the findings and in a lesser resolution of the applied buffer. The impression is that the V8Nexus system combined with the utilized buffer provides greater resolution in the alpha-1 and alpha-2 globulin fractions, but that it declines in the gamma globulin fraction. The precision and estimated accuracy criteria were met by both systems. Comparison results implied that capillary systems are not equally effective in M-protein screening, highlighting the necessity to include system screening efficiency in analytical evaluation.