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Abstract
1. This study compared the analysis of digoxin using a high-performance liquid chromatographic post-column derivatization (HPLC-PC) assay and the TDx fluorescence polarization immunoassay (FPIA).
2. Serum obtained from 15 digitalized patients showed higher mean digoxin levels with the FPIA method as compared to the HPLC-PC procedure such that the mean HPLC-PC/FPIA ratio was 0.91±0.14 (mean±SD). Demonstrated cross-reactivity of digoxin metabolites with the FPIA is probably responsible for this observation.
3. Cross-reactivity of the immunoassay towards endogenous material present in serum samples from certain patient groups was an even greater problem, with apparent ‘digoxin’ serum concentrations in untreated hepatic failure patients being within the therapeutic range for digoxin.
4. The HPLC-PC method did not suffer from such interference and would therefore provide more accurate values for patients where high levels of interference could contribute to false digoxin levels.