A dry-strip immunometric assay for digoxin on the Ames Seralyzer

We evaluated the Ames Seralyzer III with a new reagent and drystrip test for assay of digoxin. Assay precision was acceptable in the therapeutic range. Within-run imprecision (coefficient of variation, n = 20) was 7% at 0.9 ng/ml (1.2 nM) and 3.5% at 1.9 ng/ml (2.4 nM); run-to-run imprecision was 7.6% at 0.8 ng/ml (1.0 nM) and 5.7% at 2.1 ng/ml (2.7 nM). The method is very reproducible and is linear between 0.5 and 4.3 ng/ml (0.6-5.5 nM). The assay performed well with patient samples, with Abbott TDx used as the reference procedure. Bilirubin up to 16 mg/dl (273 microM) and hemoglobin up to 11 g/l do not cause interference. Digoxin-like immunoreactive factors cause minimal interference. Some digoxin metabolites such as monodigitoxoside, bis-digitoxoside, and digoxigenin cross-react with the digoxin antibody. Patients on spironolactone have falsely increased digoxin values. The new digoxin assay is easy to perform and uses 30 microliters serum; the result can be reported in 15-20 min.