Table 1 Detection of monoclonal protein using mass spectrometry assays among patients considered not to have monoclonal gammopathy of undetermined significance (MGUS) in the Olmsted Screening Study, but subsequently developed the disorder during follow-up.

Baseline samples considered negative for MGUS by serum protein electrophoresis and serum-free light-chain assay

 Number of patients tested

226

226

226

 Number of patients with detectable monoclonal protein, (%)

24 (10.6)

113 (50.0)

149 (65.9)

Samples from time of clinical MGUS diagnosis

 Number of patients tested

226

226

221

 Number of patients with detectable monoclonal protein, (%)

226 (100)^a

188 (83.2)

200 (90.5)