Serum protein electrophoresis: a retrospective audit of migration patterns and paraprotein concentrations

Introduction: Serum protein electrophoresis (SPEP) is, in part, used for the detection of paraproteins. The Department of Pathology, Royal Hobart Hospital undertakes SPEP and immunofixation for both in- and outpatients. Results were retrospectively audited, in particular the relationship between the paraprotein concentration measured by SPEP and the immunoglobulin concentration measured by nephelometry, and the electrophoretic region that the paraprotein migrated in.

Methods: Patient demographics, total protein, albumin, IgA, IgG, IgM and paraprotein concentration, together with any interpretive comments, were extracted from the laboratory information system; 2010-2020. Protein electrophoresis was undertaken using the Sebia Hydrasys gel electrophoresis system. Total protein, albumin, IgA, IgG, and IgM were measured by nephelometry.

Results: There were 3490 samples analysed over the audit period. A paraprotein (2757) was detected in 65% of samples. IgG kappa/lambda, IgM kappa/lambda, IgA kappa/lambda, and IgD kappa/lambda were detected in 1,203/612, 294/158, 179/96, and 6/6 instances, respectively. IgE kappa/lambda were not detected. All IgG paraproteins migrated within the gamma-region, 90 % of IgM paraproteins migrated within the gamma/gamma-beta-region, 47% and 41% of IgA paraproteins migrated in the gamma- and beta-regions, respectively. Immunoglobulin D paraproteins largely (70%) migrated within the beta-region (30% in gamma-region). All paraproteins measured by nephelometry correlated well with the concentration measured by densitometry (IgG: R=0.94, IgM: R=0.93, IgA: R=0.92). The slopes for IgG and IgA paraproteins were 1.06 (95% CI 0.95-1.17) and 1.15 (95 % CI 1.13-1.17), respectively, showing a very good correspondence with quantification by nephelometry. The slope for IgM paraproteins was 1.64 (95% CI 1.53-1.75), illustrating a systematic higher result using nephelometry than SPEP.

Conclusion: Immunoglobulin G paraproteins were the most common detected. Although there was a good relationship between densitometry and nephelometry for IgG and IgA, IgM paraproteins were overestimated by densitometry.