Undetected IgM paraproteins on serum protein electrophoresis.

Sera from three patients initially evaluated by cellulose acetate electrophoresis demonstrated apparent application "artifacts." On agarose gel electrophoresis, each had a definite paraprotein "spike." The immunoglobulin classes of the paraproteins were determined by immunoelectrophoresis, with and without reduction by dithiothreitol. The immunoglobulin class was confirmed by immunofixation electrophoresis on agarose gel. All three abnormal immunoglobulins were IgM-kappa-type paraproteins. Agarose electrophoresis with immunofixation was superior in the identification of these paraproteins compared with the standard method of cellulose acetate electrophoresis coupled with immunoelectrophoresis.