The FLC dimer with lambda type may false-migrate to the position of albumin band by urine protein electrophoresis on Sebia agarose gel-based detection system

Background Monoclonal free light chains (FLC) commonly exist in monomeric or dimeric forms but rarely as larger molecules. Little is known about whether polymeric molecules can affect urine protein electrophoresis (UPE) results. Methods Urine samples were collected from 72 multiple myeloma (MM) patients with Bence Jones protein (BJP). Urine protein and immunofixation electrophoresis were analyzed on Sebia SDS agarose gel electrophoresis system (SDS-AGE), and immunoglobulin free light chains were measured on the BNII nephelometric assay. Results A type of disulfide-bound FLC dimer shows a pattern shift to the position of the albumin band in urine protein electrophoresis in multiple myeloma (MM) patients according to the Sebia agarose gel-based detection system, which was validated by immunofixation, SDS-PAGE, and mass spectrometric methods. Similar cases were found in 21 (29.17%) of 72 MM patients with BJP, and 19 (90.5%) of 21 patients were the lambda type. Conclusions These results indicate that BJP with lambda type has a strong tendency to abnormally migrate, which may increase the risk of misinterpretation of protein electrophoresis in clinics. Thus, when the urine protein electrophoresis is inconsistent with the result by nephelometric method, urine protein electrophoresis needs to be repeated on the deduced condition to confirm the essence of the originally identified albumin.