An international multi-center serum protein electrophoresis accuracy and M-protein isotyping study. Part II: Limit of detection and follow-up of patients with small M-proteins

Joannes F.M. Jacobs, Katherine A. Turner, Maria Stella Graziani, Jody L. Frinack, Michael W. Ettore, Jillian R. Tate, 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 journalArticlepeer-review

Abstract

Electrophoretic methods to detect, characterize and quantify M-proteins play an important role in the management of patients with monoclonal gammopathies (MGs). Significant uncertainty in the quantification and limit of detection (LOD) is documented when M-proteins are <10 g/L. Using spiked sera, we aimed to assess the variability in intact M-protein quantification and LOD across 16 laboratories. Sera with normal, hypo- or hyper-gammaglobulinemia were spiked with daratumumab or elotuzumab, with concentrations from 0.125 to 10 g/L (n = 62) along with a beta-migrating sample (n = 9). Laboratories blindly analyzed samples according to their serum protein electrophoresis (SPEP)/isotyping standard operating procedures. LOD and intra-laboratory percent coefficient of variation (%CV) were calculated and further specified with regard to the method (gel/capillary electrophoresis [CZE]), gating strategy (perpendicular drop [PD]/tangent skimming [TS]), isotyping (immunofixation/immunosubtraction [ISUB]) and manufacturer (Helena/Sebia). All M-proteins ≥1 g/L were detected by SPEP. With isotyping the LOD was moderately more sensitive than with SPEP. The intensity of polyclonal background had the biggest negative impact on LOD. Independent of the method used, the intra-laboratory imprecision of M-protein quantification was small (mean CV = 5.0%). Low M-protein concentration and high polyclonal background had the strongest negative impact on intra-laboratory precision. All laboratories were able to follow trend of M-protein concentrations down to 1 g/L. In this study, we describe a large variation in the reported LOD for both SPEP and isotyping; overall LOD is most affected by the polyclonal immunoglobulin background. Satisfactory intra-laboratory precision was demonstrated. This indicates that the quantification of small M-proteins to monitor patients over time is appropriate, when subsequent testing is performed within the same laboratory.

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

Keywords

  • accuracy
  • immunofixation
  • immunosubtraction
  • limit of detection
  • monoclonal proteins
  • precision
  • protein electrophoresis

ASJC Scopus subject areas

  • Clinical Biochemistry
  • Biochemistry, medical

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