Persistence of M-proteins detected by mass spectrometry

Monoclonal gammopathy of undetermined significance (MGUS) is the most common plasma cell proliferative disorder. When screened with serum protein electrophoresis (SPEP), 3% of individuals over the age of 50 have a detectable M-protein [ 1 ]. While often thought of as benign, MGUS has long-term implications such as yearly testing and concern for progression to serious disease such as multiple myeloma. Mass spectrometry (MS) detection of monoclonal proteins (M-proteins) is gaining acceptance as a method suitable for patient care [ 2 ]. In 2018, the Mayo Clinic protein immunology laboratory replaced traditional immunofixation electrophoresis (IFE) with a MALDI-TOF MS method (Mass-Fix) and has tested more than 620,000 samples. Mass-Fix is more sensitive and specific than SPEP [ 3 ], resulting in a higher MGUS prevalence (approximately 11%) in individuals older than 50 [ 4 ]. Many of these MGUS patients have M-proteins well below the level of quantitation of SPEP, which is approximately 0.1 g/dL. This study aims to summarize the persistence and clinical outcomes on MGUS related M-proteins detected by Mass-Fix.