To assess the persistence of M-proteins detected by Mass-Fix in patients with MGUS.
Approach:
Study Population: Of 6,035 patients with MGUS, 761 had at least three Mass-Fix tests spanning a minimum of 6 months.
Persistence Assessment: Persistence was defined as detection of an M-protein with the same isotype at each test and a light-chain mass within ±20 Da.
Data Analysis: Mass-Fix software estimated the M-protein percentage relative to total IgG, IgA, or IgM.
Key Findings:
M-proteins met the study’s persistence criteria in 97% of cases over at least 6 months.
Persistence was 99.8% for M-proteins comprising more than 10% of the corresponding total immunoglobulin.
Among M-proteins comprising 1–10%, 93% met the persistence criteria; persistence was lowest for low-level IgM M-proteins.
Interpretation:
In this selected cohort, most low-level M-proteins detected by Mass-Fix were repeatedly detected over the study period. These findings are consistent with persistence but do not establish that every detected M-protein is attributable to MGUS rather than a transient immune response.
Limitations:
The study did not use systematic, population-based patient sampling.
M-protein percentages were relative estimates, not absolute quantitative measurements.
Conclusion:
Most M-proteins detected by Mass-Fix in this cohort, including low-level M-proteins, met the study’s persistence criteria. Persistence alone does not establish a diagnosis of MGUS.
