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Received on July 13, 2004
Accepted on February 1, 2005
Proteomics and Protein Markers |
1 Department of Biotechnology, University of Turku, Turku, Finland
2 Department of Laboratory Diagnostics, Helsinki University Central Hospital, Helsinki, Finland
* To whom correspondence should be addressed. E-mail: susann.eriksson{at}utu.fi.
Background: There are numerous potential sources of interference in immunoassays. Our aim was to identify the blood component that causes negative interference in cardiac troponin I (cTnI) immunoassays based on antibodies against the central part of cTnI.
Methods: We isolated an interfering factor (IF) was from a sample with false low cTnI values, using several consecutive purification steps: caprylic acid precipitation, ammonium sulfate precipitation, and purification on Cibacron Blue gel and protein G columns. Purified IF was identified by gel electrophoresis and mass spectrometric analysis of protein bands. For the direct detection of human antibodies to cardiac troponin in serum samples, we developed immunoassays using three different anti-human immunoglobulin antibodies and measured troponin antibodies in samples with low and normal cTnI recovery.
Results: Treatment with caprylic acid did not precipitate IF, but IF precipitated at 40% ammonium sulfate saturation. IF bound to a Cibacron Blue gel column, from which it was eluted with a linear salt gradient. It also bound to protein G. Gel electrophoresis of purified IF showed two major bands with molecular masses corresponding to the heavy (
50 kDa) and light chains (25 kDa) of immunoglobulin, and their identities were confirmed by mass spectrometry. The presence of troponin-specific autoantibodies was confirmed in samples with low recoveries of cTnI by three different immunoassays. The median signals were significantly higher in 10 samples with low recovery than in 10 samples with normal recovery of cTnI (P
0.007).
Conclusions: Circulating autoantibodies to cTnI or other proteins of the troponin complex can be a source of negative interference in cTnI immunoassays.
The following articles in journals at HighWire Press have cited this article:
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  A A A Ismail Interference from endogenous antibodies in automated immunoassays: what laboratorians need to know J. Clin. Pathol., August 1, 2009; 62(8): 673 - 678. [Abstract] [Full Text] [PDF]
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 K. Pettersson, S. Eriksson, S. Wittfooth, E. Engstrom, M. Nieminen, and J. Sinisalo Autoantibodies to Cardiac Troponin Associate with Higher Initial Concentrations and Longer Release of Troponin I in Acute Coronary Syndrome Patients Clin. Chem., May 1, 2009; 55(5): 938 - 945. [Abstract] [Full Text] [PDF]
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P. Venge, S. James, L. Jansson, and B. Lindahl Clinical Performance of Two Highly Sensitive Cardiac Troponin I Assays Clin. Chem., January 1, 2009; 55(1): 109 - 116. [Abstract] [Full Text] [PDF]
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 F. Leuschner, J. Li, S. Goser, L. Reinhardt, R. Ottl, P. Bride, J. Zehelein, G. Pfitzer, A. Remppis, E. Giannitsis, et al. Absence of auto-antibodies against cardiac troponin I predicts improvement of left ventricular function after acute myocardial infarction Eur. Heart J., August 2, 2008; 29(16): 1949 - 1955. [Abstract] [Full Text] [PDF]
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NACB WRITING GROUP MEMBERS, A. H.B. Wu, A. S. Jaffe, F. S. Apple, R. L. Jesse, G. L. Francis, D. A. Morrow, L. K. Newby, J. Ravkilde, W.H. W. Tang, et al. National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines: Use of Cardiac Troponin and B-Type Natriuretic Peptide or N-Terminal proB-Type Natriuretic Peptide for Etiologies Other than Acute Coronary Syndromes and Heart Failure Clin. Chem., December 1, 2007; 53(12): 2086 - 2096. [Abstract] [Full Text] [PDF]
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 P. Unverir, B. C. Soner, E. Dedeoglu, O. Karcioglu, K. Boztok, and Y. Tuncok Renal and hepatic injury with elevated cardiac enzymes in Amanita phalloides poisoning: a case report Human and Experimental Toxicology, September 1, 2007; 26(9): 757 - 761. [Abstract] [PDF]
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 A. H.B. Wu Cardiac Troponin: Friend of the Cardiac Physician, Foe to the Cardiac Patient? Circulation, October 17, 2006; 114(16): 1673 - 1675. [Full Text] [PDF]
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S. James, M. Flodin, N. Johnston, B. Lindahl, and P. Venge The Antibody Configurations of Cardiac Troponin I Assays May Determine Their Clinical Performance Clin. Chem., May 1, 2006; 52(5): 832 - 837. [Abstract] [Full Text] [PDF]
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Q. Lam, M. Black, O. Youdell, H. Spilsbury, and H.-G. Schneider Performance Evaluation and Subsequent Clinical Experience with the Abbott Automated Architect STAT Troponin-I Assay Clin. Chem., February 1, 2006; 52(2): 298 - 300. [Abstract] [Full Text] [PDF]
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S. Eriksson and K. Pettersson Beliefs in Cardiac Troponin Testing Clin. Chem., September 1, 2005; 51(9): 1755 - 1756. [Full Text] [PDF]
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M. Panteghini Selection of Antibodies and Epitopes for Cardiac Troponin Immunoassays: Should We Revise Our Evidence-Based Beliefs? Clin. Chem., May 1, 2005; 51(5): 803 - 804. [Full Text] [PDF]
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S. Eriksson, T. Ilva, C. Becker, J. Lund, P. Porela, K. Pulkki, L.-M. Voipio-Pulkki, and K. Pettersson Comparison of Cardiac Troponin I Immunoassays Variably Affected by Circulating Autoantibodies Clin. Chem., May 1, 2005; 51(5): 848 - 855. [Abstract] [Full Text] [PDF]
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