Improved liquid chromatographic/immunoassay of digoxin in serum

This HPLC/immunoassay procedure measures digoxin in serum with no interference from digoxin metabolites or digoxin-like factors. We used solid-phase (C18 and Diol) extraction, a C18 column with a tetrahydrofuran/water mobile phase, and final quantification by fluorescence polarization immunoassay. Deslanoside and gitoxigenin were used as the internal standard and the retention-time marker, respectively. The average CV for 300-microL samples at digoxin concentrations between 0.9 and 3.9 nmol/L was 9.3%. Minimum column lifetime with daily use was three months. We also compared results, for 49 samples from patients taking digoxin, obtained with the Abbott "TDx FPIA digoxin I" and the present procedure. Discrepancies between the two methods were substantial for 20% of the samples.