Evaluation of inter-method and inter-observer variability in the quantification of paraproteins by serum protein electrophoresis

Abstract Objectives Serum protein electrophoresis is a widely used technique for the detection of multiple myeloma and other serum protein disorders. Paraprotein quantification can be performed using either the perpendicular drop or the tangent skimming method. The aim of this study was to evaluate both methods and to investigate inter-observer variability in the quantification of paraproteins in serum samples analysed by capillary zone electrophoresis. Methods Laboratory data from serum protein electrophoresis performed by capillary zone electrophoresis between October 1 and December 31, 2024 were reviewed. Patients aged 18–100 years were included in the study. Paraprotein quantification results were evaluated independently by three clinical biochemists using both perpendicular drop or the tangent skimming quantification methods. Results Paraprotein levels quantified by the perpendicular drop method were significantly higher than those quantified by the tangent skimming method across all three observers (p<0.001 for all). A very strong correlation was observed between the two methods for each observer (r=0.92, r=0.93, and r=0.93; p<0.001 for all). A discrepancy was observed between observers 1 and 2 in hypergammaglobulinemic samples using both methods. However, observer 3 consistently reported higher paraprotein levels than observers 1 and 2 using both methods (p<0.05 for all). Conclusions Although serum protein electrophoresis is an established laboratory technique, a lack of standardization persists in result reporting across laboratories. Switching between quantification methods during patient follow-up is not recommended. It is recommended that using the same method, the same laboratory, and ideally the same clinical biochemist for result interpretation.