Fluoroimmunoassay of Digoxin in Serum

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Abstract
A heterogeneous (solid-phase separation) fluoroimmunoasssay for digoxin [a cardiac glycoside] in human serum was developed employing antibodies coupled to magnetizable cellulose/iron oxide particles and a fluorescein-labeled digoxin derivative as tracer. Intrinsic fluorophores and other potentially interfering components of serum samples were reliably and completely removed at the separation and wash steps of the assay procedure which were facilitated by magnetic sedimentation. To attain adequate sensitivity (detection limit 0.2 .mu.g/l (0.26 nmol/l) serum digoxin), a sample volume of 500 .mu.l was necessary. Assay results for patients'' specimens correlated well with those obtained using established charcoal-separation (r = 0.96) and magnetizable solid-phase (r = 0.95) radioimmunoassays. The feasibility of a stat adaptation of the fluoroimmunoassay that involved only 2 standards (0.5 and 4 .mu.g/l digoxin) was demonstrated. The stat method would be suitable for the assay of urgent or single specimens.