Electrophoresis and densitometry of serum and urine in the investigation and significance of monoclonal immunoglobulins.

About 15% of monoclonal components or paraproteins are associated with malignancy when detected by simple electrophoresis on cellulose acetate membranes or agarose gel followed by protein staining. More sensitive methods for detecting monoclonal components result in a lower frequency of association with recognisable underlying disease. The sensitivity is dependent on the system used. Isoelectric focusing is 10 to 40 times more sensitive than simple electrophoresis at detecting monoclonal components. Electrophoretically separated bands may be quantitated densitometrically and at the present time this is the most satisfactory method for measuring monoclonal component concentration. Immunochemical methods for quantitating monoclonal components are limited by failure to react in a similar manner to polyclonal standards and giving problems of antigen excess resulting both in falsely elevated and low results. Electrophoretic methods must always be used in conjunction with these. The normal polyclonal ratio of immunoglobulin kappa:lambda light chain is disturbed by the presence of a monoclonal component. In 260 patients with myeloma we found that serum electrophoresis alone detected 90% while a disturbance in the kappa:lambda ratio detected 98%. However, 50% of monoclonal components less than 3 g/L were missed. Log kappa:lambda ratio correlates well with the densitometric scan of monoclonal components, both in vitro and in patients being monitored for treatment response in myeloma. This approach may complement or even replace densitometry for this purpose in the future.