Clin Chem Lab Med. 2025 Dec 3. doi: 10.1515/cclm-2025-0894. Online ahead of print.
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.
PMID:41328877 | DOI:10.1515/cclm-2025-0894