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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

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Comparison of serum digoxin concentration monitoring by fluorescence polarization immunoassay on the TDxFLx® and dry chemistry enzyme immunoassay on the Vitros 950

Bogdan Solnica1


Corresponding author: Bogdan Solnica, Diagnostic Division, Department of Clinical Biochemistry, Jagiellonian University, Collegium Medicum, 15b Kopernika Street, 31-501 Krakow, Poland. Phone/Fax: +48124248361, E-mail:

Citation Information: Clinical Chemistry and Laboratory Medicine. Volume 42, Issue 8, Pages 958–964, ISSN (Print) 1434-6621, DOI: 10.1515/CCLM.2004.156, August 2004

Publication History

February 17, 2004
April 19, 2004


The aim of the study was to compare the results of digoxin assays performed using fluorescence polarization immunoassay (FPIA) on the TDxFLx® and a dry chemistry enzyme immunoassay (EIA) on the Vitros 950. Within-run CV amounted to 8.52–10.49% for FPIA and 2.47–5.39% for EIA. Between-run CV amounted to 6.41–8.97% for FPIA and 3.40–5.04% for EIA. Analytical bias ranged from 2.57–4.0% for FPIA and from 9.86–11.9% for EIA. In comparative studies the correlation coefficient was 0.878; Deming regression analysis yielded a slope of 1.057 (95% CI: 0.573 to 1.541) and intercept of 0.078 (95% CI: –0.391 to 0.547), and the Passing-Bablok agreement test yielded a slope of 1.111 (95% CI: 0.988 to 1.212) and intercept of 0.094 (95% CI: –0.018 to 0.182). The mean digoxin concentration in patients’ sera measured by EIA was significantly higher than that measured by FPIA (1.347 vs. 1.196 ng/ml, p < 0.02). The mean absolute difference between results amounted to 0.146 ng/ml (95% CI: 0.0261 to 0.266). In comparison to EIA, FPIA yielded a higher number of subtherapeutic concentrations < 0.5 ng/ml (29.7% vs. 21.8%) and a lower number of digoxin concentrations > 1.2 ng/ml (25.7% vs. 35.6%). These discrepancies occurred in approximately 10% of samples. The obtained results showed different analytical performance and method-dependent differences in the distribution of results. This indicates the necessity to harmonize digoxin immunoassays if two different analytical systems are used in the same clinical setting.

Keywords: digoxin; dry chemistry; enzyme immunoassay; fluorescence polarization immunoassay; therapeutic drug monitoring

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