An international multi-center serum protein electrophoresis accuracy and M-protein isotyping study. Part I: Factors impacting limit of quantitation of serum protein electrophoresis

Katherine A. Turner, Jody L. Frinack, Michael W. Ettore, Jillian R. Tate, Maria Stella Graziani, Joannes F.M. Jacobs, Ronald A. Booth, Christopher R. McCudden, David F. Keren, Julio C. Delgado, Galina Zemtsovskaja, Robert O. Fullinfaw, Anna Caldini, Theo De Malmanche, Katina Katakouzinos, Matthew Burke, Giovanni Palladini, Sara Altinier, Martina Zaninotto, Gabriella RighettiMarie Therese Melki, Stephen Bell, Maria Alice Vieira Willrich

Research output: Contribution to journalArticle

Abstract

Serum protein electrophoresis (SPEP) is used to quantify the serum monoclonal component or M-protein, for diagnosis and monitoring of monoclonal gammopathies. Significant imprecision and inaccuracy pose challenges in reporting small M-proteins. Using therapeutic monoclonal antibody-spiked sera and a pooled beta-migrating M-protein, we aimed to assess SPEP limitations and variability across 16 laboratories in three continents. Sera with normal, hypo- or hypergammaglobulinemia were spiked with daratumumab, Dara (cathodal migrating), or elotuzumab, Elo (central-gamma migrating), with concentrations from 0.125 to 10 g/L (n = 62) along with a beta-migrating sample (n = 9). Provided with total protein (reverse biuret, Siemens), laboratories blindly analyzed samples according to their SPEP and immunofixation (IFE) or immunosubtraction (ISUB) standard operating procedures. Sixteen laboratories reported the perpendicular drop (PD) method of gating the M-protein, while 10 used tangent skimming (TS). A mean percent recovery range of 80%-120% was set as acceptable. The inter-laboratory %CV was calculated. Gamma globulin background, migration pattern and concentration all affect the precision and accuracy of quantifying M-proteins by SPEP. As the background increases, imprecision increases and accuracy decreases leading to overestimation of M-protein quantitation especially evident in hypergamma samples, and more prominent with PD. Cathodal migrating M-proteins were associated with less imprecision and higher accuracy compared to central-gamma migrating M-proteins, which is attributed to the increased gamma background contribution in M-proteins migrating in the middle of the gamma fraction. There is greater imprecision and loss of accuracy at lower M-protein concentrations. This study suggests that quantifying exceedingly low concentrations of M-proteins, although possible, may not yield adequate accuracy and precision between laboratories.

Original languageEnglish
JournalClinical Chemistry and Laboratory Medicine
DOIs
Publication statusAccepted/In press - Jan 1 2020

Keywords

  • accuracy
  • immunofixation
  • immunosubtraction
  • limit of quantitation
  • monoclonal proteins
  • protein electrophoresis

ASJC Scopus subject areas

  • Clinical Biochemistry
  • Biochemistry, medical

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    Turner, K. A., Frinack, J. L., Ettore, M. W., Tate, J. R., Graziani, M. S., Jacobs, J. F. M., Booth, R. A., McCudden, C. R., Keren, D. F., Delgado, J. C., Zemtsovskaja, G., Fullinfaw, R. O., Caldini, A., De Malmanche, T., Katakouzinos, K., Burke, M., Palladini, G., Altinier, S., Zaninotto, M., ... Willrich, M. A. V. (Accepted/In press). An international multi-center serum protein electrophoresis accuracy and M-protein isotyping study. Part I: Factors impacting limit of quantitation of serum protein electrophoresis. Clinical Chemistry and Laboratory Medicine. https://doi.org/10.1515/cclm-2019-1104