Will any monoclonal proteins detected by SPE and/or IFE be missed by sFLC tests?
Yes. Monoclonal proteins can be intact immunoglobulins or FLCs. Since sFLC assays are >100 times more sensitive than electrophoretic tests it is most unlikely that FLCs will be detected in serum by SPE or IFE yet be normal by FLC assays. However, intact immunoglobulin monoclonal immunoglobulins by tradition (especially MGUS) are detected by IFE and SPE, but may have normal FLC concentrations. Studies indicate that all LCMM and ~95% of AL amyloidosis patients are correctly identified by sFLC assays.
