Differences identified between serum and urine immunofixation electrophoresis

Background: Different patterns between serum immunofixation electrophoresis (SIFE) and urine immunofixation electrophoresis (UIFE) happen occasionally and laboratorians should understand the mechanisms behind the differences and additional tests required for complicated cases.

Methods: We investigated a complicated multiple myeloma case that showed inconsistent patterns of SIFE and UIFE. To differentiate monoclonal proteins (M-proteins), the urine sample was treated with dithiothreitol to open up the IgA molecule and urine free light chain assay was used for free light chain analysis.

Results: The patient's SIFE indicated 2 IgA λ and 1 IgM κ M-proteins, while UIFE revealed monoclonal free λ light chains and a suspicious monoclonal IgA κ protein. Subsequent treatment of the urine sample with dithiothreitol and urine free light chain assay demonstrated that the suspicious monoclonal IgA κ protein was actually a monoclonal IgA λ and a free κ light chain that had similar electrophoretic mobility.

Conclusions: The differences identified between SIFE and UIFE in this case are due to the limitation of immunofixation electrophoresis on different specimen types and intra-molecular disulfide bonds formation in IgA. The laboratorians must be cognizant of the strengths and limitations of the procedure being performed and the ancillary testing techniques available to solve the problem.