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

Author:

Turner Katherine A.1,Frinack Jody L.1,Ettore Michael W.1,Tate Jillian R.2,Graziani Maria Stella3,Jacobs Joannes F.M.4,Booth Ronald A.5,McCudden Christopher R.5,Keren David F.6,Delgado Julio C.7,Zemtsovskaja Galina8,Fullinfaw Robert O.9,Caldini Anna10,de Malmanche Theo11,Katakouzinos Katina12,Burke Matthew2,Palladini Giovanni13,Altinier Sara14,Zaninotto Martina14,Righetti Gabriella15,Melki Marie Therese16,Bell Stephen17,Willrich Maria Alice Vieira18

Affiliation:

1. Department of Laboratory Medicine and Pathology , Mayo Clinic , Rochester , MN , USA

2. Department of Chemical Pathology , Pathology Queensland, Royal Brisbane and Women’s Hospital , Brisbane , QLD , Australia

3. Section of Clinical Biochemistry , University of Verona , Verona , Italy

4. Department of Laboratory Medicine , Radboud University Medical Center, Laboratory Medical Immunology , Nijmegen , the Netherlands

5. Department of Pathology and Laboratory Medicine , The Ottawa Hospital , Ottawa , ON , Canada

6. University of Michigan , Ann Arbor , MI , USA

7. ARUP Laboratories, Department of Pathology , University of Utah School of Medicine , Salt Lake City , UT , USA

8. Clinical Chemistry Laboratory , North Estonia Medical Centre , Tallinn , Estonia

9. Department of Chemical Pathology , The Royal Melbourne Hospital , Melbourne, Victoria , Australia

10. General Laboratory , Careggi University Hospital , Florence , Italy

11. NSW Health Pathology, Immunology Department , John Hunter Hospital , New Lambton Heights , NSW , Australia

12. Immunopathology Department , Royal Prince Alfred Hospital , Missenden Rd , Camperdown , NSW , Australia

13. Amyloidosis Research and Treatment Center, Foundation IRCCS Policlinico San Matteo, and Department of Molecular Medicine, University of Pavia , Pavia , Italy

14. Laboratory Medicine of the University Hospital of Padova , Padova , Italy

15. Clinical Chemistry Laboratory , University of Verona , Verona , Italy

16. Sebia Inc. , Lisses , France

17. Helena Biosciences Europe , Gateshead , UK

18. Division of Clinical Biochemistry and Immunology, Department of Laboratory Medicine and Pathology , Mayo Clinic , 200 First Street SW , Rochester, MN 55905 , USA

Abstract

Abstract Background 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. Methods 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. Results 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. Conclusions This study suggests that quantifying exceedingly low concentrations of M-proteins, although possible, may not yield adequate accuracy and precision between laboratories.

Publisher

Walter de Gruyter GmbH

Subject

Biochemistry (medical),Clinical Biochemistry,General Medicine

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