From a review of seven different studies, it was reported that immunofixation electrophoresis (IFE) of serum and/or concentrated urine identified a small monoclonal protein in between 24 - 72% of patients with SPB . When present, a monoclonal protein can be useful for guiding therapy. In most patients, the monoclonal protein is markedly reduced upon completion of local radiotherapy but it only disappears entirely in a minority of patients. Persistence of the monoclonal protein may indicate the presence of a tumour outside the field of radiotherapy . The potential utility of sFLC analysis has been investigated in a growing number of studies, the most comprehensive of which was performed retrospectively by Dingli et al.  at the Mayo Clinic. Of 116 patients with a serum sample taken at diagnosis and prior to any therapy, the κ/λ sFLC ratio was abnormal in 54 (47%). Three smaller studies have reported abnormal κ/λ sFLC ratios in 30 - 68% of patients at diagnosis .