Detection and identification of serum monoclonal immunoglobulin by immunoisoelectric focusing. Limits of sensitivity and use during relapse of multiple myeloma.

The limits of detection of four classes of monoclonal immunoglobulin and free light chain in serum by isoelectric focusing and immunoisoelectric focusing have been determined and the sensitivity of these techniques compared with that obtained using immunoelectrophoresis and zonal electrophoresis with immunofixation. Immunoisoelectric focusing was 10-40 times more sensitive than immunoelectrophoresis and could be used to detect concentrations of monoclonal immunoglobulin that were undetectable by zonal electrophoresis with immunofixation. The relevance of this work in monitoring multiple myeloma during treatment and relapse is discussed.