Rapid plasma digoxin assay in outpatients--a useful routine technique?

In 25 outpatients taking digoxin for chronic atrial fibrillation (established for at least six months) a prospective study identified only one case in which rapid availability of the results of a plasma digoxin assay altered the dose which had already been selected on the basis of simple clinical assessment. No patient received more than 375 micrograms digoxin per day and none showed clinical evidence of toxicity even though seven had renal impairment. Six other patients had poorly controlled ventricular rates requiring larger doses of digoxin, but even in these patients the dose could be selected on clinical grounds alone. Despite the availability of a very rapid fluorescence polarisation immunoassay for digoxin, simple but careful clinical monitoring is an adequate basis for the selection of a suitable dose in most patients taking digoxin for atrial fibrillation.