Detection of monoclonal plasma cells in the peripheral blood of patients with primary amyloidosis

We evaluated the blood from 150 patients with primary AL-amyloidosis for circulating monoclonal plasma cells using a sensitive slide-based immunofluorescence technique. The percentage of monoclonal blood plasma cells (BPC) that were in S-phase was determined by the bromodeoxyuridine labelling index (BLI). Monoclonal BPC were detected in 16% (24/150) of patients. The median number of monoclonal BPC was 1 × 10⁶/l and 4.6% (7/150) of patients had a high number. The BLI was zero in all but three patients. This study demonstrates that monoclonal plasma cells circulate in the peripheral blood of patients with AL-amyloidosis.