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Clinical Chemistry and Laboratory Medicine (CCLM)

Published in Association with the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM)

Editor-in-Chief: Plebani, Mario

Ed. by Gillery, Philippe / Lackner, Karl J. / Lippi, Giuseppe / Melichar, Bohuslav / Schlattmann, Peter / Tate, Jillian R. / Tsongalis, Gregory J.

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Detection of serum free light chains: the problem with antigen excess

Markus Bosmann1, 2, a / Jürgen Kößler2, a / Herbert Stolz2 / Ulrich Walter2 / Stefan Knop3 / Udo Steigerwald2

1Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA

2Laboratory Medicine, Institute of Clinical Biochemistry and Pathobiochemistry, University of Wuerzburg, Germany

3Division of Hematology and Medical Oncology, Department of Internal Medicine II, University Hospital Wuerzburg, Germany

aM. Bosmann and J. Kößler contributed equally to this work.

Corresponding author: Markus Bosmann, MD, Department of Pathology, University of Michigan Medical School, Room 7526, MSRBI, Box 5602, 1150 West Medical Center Drive, Ann Arbor, MI 48109-5602, USA Phone: +734 647 2929, Fax: +734 764 4308,

Citation Information: Clinical Chemistry and Laboratory Medicine. Volume 48, Issue 10, Pages 1419–1422, ISSN (Online) 1437-4331, ISSN (Print) 1434-6621, DOI: 10.1515/CCLM.2010.283, July 2010

Publication History

Received:
2010-02-04
Accepted:
2010-04-21
Published Online:
2010-07-14

Abstract

Background: In recent years, measurement of serum immunoglobulin free light chains (FLCs) has greatly facilitated diagnosis and monitoring of various plasma cells dyscrasias, including multiple myeloma. Detection of FLCs by nephelometry depends on the formation of immune complexes. However, it is known that if the antigen (free light chain) is present in great excess, non-precipitating immune complexes can be formed and be detected poorly. This may lead to inaccurate test results.

Methods: Serum samples from 91 patients were subjected prospectively to the detection of free κ and λ light chains by automated nephelometry. A standard dilution of 1:100 was paralleled by a 1:2000 dilution. In addition, samples with values below the effective range (1:100) were subjected to a 1:20 dilution in order to calculate the κ/λ ratio.

Results: Here, we report the incidence of antigen excess in a cohort of 91 patients with a high proportion of monoclonal abnormalities. A standard dilution (1:100) of free light κ chains from a patient with monoclonal immunoglobulin A κ gammopathy were missed repeatedly. In a second patient (with myeloproliferative disease and an apparent incidental FLC monoclonal gammopathy of undetermined significance) free λ chains were also substantially underestimated in the standard dilution. Hence, the incidence of erroneously low test results due to antigen excess was 2.20%.

Conclusions: We found a significantly higher incidence of falsely low test results due to antigen excess than reported previously. Antigen excess may result in erroneous interpretations in sera subjected to nephelometric analysis. Therefore, clinical decisions should not be based solely on a single assay, especially if FLC testing includes only one dilution of the serum sample. Instead, several parallel dilutions should be recommended for screening of patients.

Clin Chem Lab Med 2010;48:1419–22.

Keywords: antigen excess; hook effect; multiple myeloma; nephelometry; serum free light chains

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