Extended verification of an automated MALDI-TOF mass spectrometry system for high throughput serum M-protein measurement

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Abstract
Objectives: This study aimed to perform an extended analytical verification of the Immunoglobulin Isotypes (GAM) for the EXENT ® Analyzer (EXENT ® -GAM) assay, a MALDI-TOF mass spectrometry-based method for detecting and quantifying serum M-proteins in patients with plasma cell dyscrasias, and to compare it with conventional serum protein electrophoresis (SPEP), serum immunofixation electrophoresis (sIFE) and serum free light chains (sFLC) assays. Methods: Imprecision, linearity, limit of quantification (LOQ), quantification comparison with SPEP, isotyping concordance with sIFE and sFLC, interference from therapeutic monoclonal antibodies (t-mAbs), sample stability, and reagent lot consistency were evaluated. Results: EXENT ® -GAM demonstrated acceptable imprecision (CV ≤20 % for low and ≤15 % for high M-protein levels) and wide linear range (∼0.03–30 g/L). The polyclonal immunoglobulin background negatively influenced the assays LOQ. M-proteins with mass-shifted light chains (i.e., glycosylated light chains) are prone to non-linearity and inferior LOQ. M-protein quantification by EXENT ® differed systematically and proportionally from quantification by SPEP, highlighting non-interchangeability. EXENT ® demonstrated 97 % concordance with sIFE for M-protein isotyping and identified numerous additional (low-level) M-proteins. Some proved to be clinically relevant (residual disease in sIFE-negative samples); others lacked correlation with sFLC result or clinical diagnosis. EXENT ® reliably distinguished endogenous M-proteins from t-mAbs, except talquetamab, which interfered with quantification and was partially misclassified. Conclusions: EXENT ® -GAM enables sensitive and reproducible quantification and isotyping of M-proteins below the detection limit of SPEP and sIFE. Its ability to resolve analytical challenges posed by SPEP and sIFE represents a significant advancement. Further clinical studies are needed to confirm its potential in residual disease detection.

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