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Clinical Chemistry 51: 848-855, 2005. First published February 17, 2005; 10.1373/clinchem.2004.040089
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Right arrow Proteomics and Protein Markers
(Clinical Chemistry. 2005;51:848-855.)
© 2005 American Association for Clinical Chemistry, Inc.

Proteomics and Protein Markers

Comparison of Cardiac Troponin I Immunoassays Variably Affected by Circulating Autoantibodies

Susann Eriksson1,a, Tuomo Ilva2, Charlotte Becker3, Juha Lund2, Pekka Porela2, Kari Pulkki4, Liisa-Maria Voipio-Pulkki5 and Kim Pettersson1

Departments of1 Biotechnology and 2 Medicine, University of Turku, Turku, Finland.
3 Department of Laboratory Medicine, Division of Clinical Chemistry, Malmö University Hospital, Malmö, Sweden.
Departments of4 Laboratory Diagnostics and 5 Medicine, Helsinki University Central Hospital, Helsinki, Finland.

aAddress correspondence to this author at: Department of Biotechnology, University of Turku, Tykistökatu 6A, FIN-20520 Turku, Finland. Fax 358-2-333-8050; e-mail susann.eriksson{at}utu.fi.

Background: We recently provided evidence that circulating autoantibodies against cardiac troponin I (cTnI) or the troponin complex cause negative interference in cTnI immunoassays. By comparing three cTnI immunoassays, we further explored the phenomenon of circulating autoantibodies and their consequences in patient samples.

Methods: We developed a cTnI immunoassay with a novel assay design using three antibodies, two of which bind epitopes outside the stable, central part of cTnI. Samples from 541 chest pain patients were measured with the new cTnI assay and with a first-generation cTnI assay (Innotrac Aio cTnI) using a conventional midfragment assay design. Using another sample cohort, we also compared the new assay with a second-generation cTnI assay (Access AccuTnI).

Results: The analytical detection limit of the new cTnI assay was 0.012 µg/L, and the lowest concentration giving a total imprecision (CV) of 10% was 0.060 µg/L. The mean difference (95% limits of agreement) between the new cTnI and Aio cTnI assays was larger in admission samples (21.0%; –107.8% to 149.7%) than in samples taken 6–12 h (12.8%; –61.5% to 87.2%) and 24 h after admission (3.0%; –71.3% to 77.4%; P <0.001). With the lowest concentrations giving 10% CV (0.22 µg/L for Aio cTnI) used as cutoffs, 14.3% (n = 76) of admission samples were positive only with the new assay, whereas 13.5% (n = 72) were positive with both assays. Of samples taken at 6–12 and 24 h, 10.2% (n = 31) and 8.3% (n = 29) were positive only with the new assay. ROC curve analysis of admission samples showed a significantly higher area under the curve for the new cTnI assay (0.940) than for the Aio cTnI assay (0.846; P <0.001). The new cTnI assay gave generally lower results than the AccuTnI assay; the mean (95% limits of agreement) differences were –58.9% (–151.8% to 34.0%) in admission samples. In samples with severe interference from autoantibodies, median ratios between the new assay and AccuTnI were higher than in samples with no apparent troponin autoantibodies (0.875 vs 0.481; P<0.001).

Conclusions: The new cTnI assay, which is based on a novel antibody combination different from the conventional midfragment antibody approach, offers improved detection of cTnI in samples containing troponin autoantibodies.




The following articles in journals at HighWire Press have cited this article:


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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
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Q. Lam, M. Black, O. Youdell, H. Spilsbury, and H.-G. Schneider
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S. Eriksson and K. Pettersson
Beliefs in Cardiac Troponin Testing
Clin. Chem., September 1, 2005; 51(9): 1755 - 1756.
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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.
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S. Eriksson, H. Halenius, K. Pulkki, J. Hellman, and K. Pettersson
Negative Interference in Cardiac Troponin I Immunoassays by Circulating Troponin Autoantibodies
Clin. Chem., May 1, 2005; 51(5): 839 - 847.
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