Immunofixation as an adjunct to immunoelectrophoresis in characterization of serum monoclonal immunoglobulins.

We evaluated quantitatively the usefulness of immunofixation (IF) as an adjunct to immunoelectrophoresis (IEP) in characterizing serum monoclonal proteins. In 33 out of 97 consecutive patients with one or more homogeneous bands on cellulose acetate serum protein electrophoresis, a monoclonal immunoglobulin could not be characterized with certainty by IEP. Of these 33 cases, in 76% a monoclonal immunoglobulin was subsequently characterized by IF on agarose gel. In 18% IF provided additional suggestive information, and in 6% it provided no additional or less information than IEP. The mean concentration of monoclonal proteins (other than free light chains) that could be characterized by IEP was 25 g/l. The monoclonal proteins that required IF for characterization were all less than 10 g/l. Of all monoclonal proteins below 10 g/l, 53% required IF for complete characterization. IF is a useful adjunct to IEP, primarily in cases where the concentration of monoclonal immunoglobulin is less than 10 g/l.