Monoclonal Immunoglobulin Associated with Monoclonal Free Light Chains Invisible on Capillary Electrophoresis.

Background: We report the case of a monoclonal immunoglobulin of IgM Lambda isotype associated with monoclonal lambda-type free light chains not detected by capillary electrophoresis but identified by immunofixation.

Methods: Capillary electrophoresis showed hypoproteinemia and an inflammatory syndrome. The IF realized on Hydrasys 2 Scan Focusing Sebia® reveals an IgM monoclonal band and two monoclonal bands in the total lambda. A second IF is performed using anti IgM, anti IgD, anti IgE and anti-total and -free lambda light chains as antisera. It reveals the presence of a monoclonal protein isotype IgM Lambda with free light chains. In view of these discordant results, an immunosubtraction was performed on the same sample showing no abnormality.

Results: Our patient has a monoclonal IgM Lambda with lambda monoclonal free light chains all masked on capillary electrophoresis and therefore not detected.

Conclusions: Capillary electrophoresis techniques are incrementally becoming the techniques of choice in medical laboratories as a replacement for gel electrophoresis, due to their automation and better sensitivity. However, in some cases, a monoclonal immunoglobulin may not be detected by capillary technique and may cause an inaccurate interpretation.