Detection of clonal plasma cells by NGF cytometry stratifies MGUS outcomes. Kaplan-Meier analysis of (A) the probability of persistent M-protein (as detected by either SPEP or immunofixation) and (B) cumulative incidence of progression to a more advanced plasma cell disorder, comparing MGUS individuals with detectable (n = 72; blue) vs undetectable (n = 19; red) clonal plasma cells by NGF cytometry.