Does a specific radioimmunoassay accurately differentiate between therapeutic and toxic serum digoxin concentrations in patients receiving digoxin?
A newly developed radioimmunoassay can rapidly and accurately distinguish between therapeutic and toxic serum digoxin levels, aiding in the clinical evaluation of digitalization.
A sensitive (0.2 ng per milliliter), precise (standard deviation 3 to 4 per cent), and specific radioimmunoassay for serum digoxin concentration has been developed. Levels are determined by measurement of the extent to which digoxin in the patient's serum competes with tritium-labeled digoxin, added in vitro, for digoxin-specific antibody binding sites. Mean values in nontoxic patients with normal renal function receiving 0.25 or 0.50 mg per day were 1.1 and 1.4 ng per milliliter respectively; the ranges fell within relatively narrow limits. Patients with cardiac arrhythmias attributed to digoxin toxicity had a mean level of 3.3 ng per milliliter, and little overlap with the nontoxic group (p less than 0.001). A determination can be completed in one hour, and may provide useful information to the clinician faced with the difficult problem of evaluating his patient's state of digitalization.
Smith et al. (1969) studied this question.