Paradigm Shift in Monoclonal Protein Detection: From Electrophoresis-based to Mass Spectrometry–based Methods

Monoclonal protein (M-protein) is a crucial biomarker for diagnosing and monitoring monoclonal gammopathies, including multiple myeloma (MM). Traditionally, electrophoresis (EP)-based methods, such as protein EP and immunofixation EP, have been widely used for M-protein detection. However, these methods can show low sensitivity and inadequate quantification of small amounts of M-protein. To overcome these challenges, EP-based methods are often combined with the quantification of serum free light chains in automated immunoassays. Advances in mass spectrometry (MS) have introduced three main approaches for sample preparation: top-down, middle-down, and bottom-up. Middle-down approaches are commonly used with matrix-assisted laser desorption/ionization time-of-flight MS and liquid chromatography-electrospray ionization (LC-ESI) quadrupole time-of-flight MS, whereas the bottom-up approach is typically applied with LC-ESI Orbitrap MS. A review of studies, conducted from 2014 to 2024, on plasma cell disorders that utilized MS-based methods demonstrate improvements in the sensitivity and accuracy of M-protein identification and quantification. MM remains the most frequently studied disease, with significant therapeutic advancements leading to improved outcomes. Minimal residual disease has gained attention because of its correlation with better prognoses. Monoclonal gammopathy of undetermined significance and amyloid light-chain amyloidosis are occasionally addressed, while studies on other rare diseases remain limited. This review highlights the clinical applications and advancements in MS-based methods, particularly in assessing M-protein levels for treatment responses, risk factors, and prognostic monitoring. Given their advantages-high sensitivity and specificity, automation, cost-effectiveness, and time efficiency-MS-based methods may eventually replace EP-based methods in clinical laboratories.