Capillary Electrophoresis Not Detecting Elevated Concentrations of Monoclonal Free Light Chains

The most common exam ordered when monoclonal gammopathy (MG) is suspected is serum protein electrophoresis (SPEP). Capillary Zone Electrophoresis (CZE) is commonly used for its automation and speed. It is well known that it fails to detect free light chains because of lower concentrations falling below CZE sensitivity. We report a case of a serum sample of a 69-year-old woman during the follow-up of a free light chain multiple myeloma. CZE was normal while serum FLC-Kappa was elevated at 6392 mg/L. Serum Immunofixation (SIFE) revealed free lights kappa chains. Capillary immunotyping showed no abnormalities. This observation highlights the limitations of CZE to detect FLC even when they are elevated and the need to avoid CZE alone. Compliance with recent guidelines by combining exams for screening, diagnosis and follow-up for MG is essential.