ASSESSMENT OF THE IMMUNOREACTIVITY OF DIGOXIN METABOLITES AND THE CROSS-REACTIVITY WITH DIGOXIN-LIKE IMMUNOREACTIVE FACTORS IN THE ROCHE-TDM ONLINE DIGOXIN ASSAY

Immunoassays for digoxin measurement have long had the problem of low specificity. Antisera used in these assays may not only measure digoxin and the active metabolites but also cross-react with the noncardioactive metabolites and digoxin-like immunoreactive factors (DLIFs). In this study, we describe the analytical performance of the newly introduced Roche-TDM ONLINE digoxin assay on the COBAS FARA II centrifugal analyzer. The assay possessed linearity up to 5.0 ng/ml, sensitivity of 0.19 ng/ml, average recovery of 100.4%, and day-to-day variability of <6%. The assay demonstrated no cross-reactivity with DLIFs or spironolactone and its metabolites and negligible reactivity with the digoxin noncardioactive metabolites. In addition, the immunoreactivity of the digoxin active metabolites reflected their cardioactivity. We conclude that the Roche-TDM ONLINE digoxin assay is highly specific and precise and suitable for the therapeutic monitoring of this drug.