Evaluation of the clinical use of serum digoxin radioimmunoassays

Of 2,586 consecutive patients admitted to a private general teaching hospital, 370 (14 percent) received digoxin therapy. Serum digoxin assays were performed on 261 of these 370 subjects. In a representative sample of 97 patients, 61 attending physicians were responsible for their care. The mean and median age of the patients was 70 years (range, 39-96 years), and one-quarter of them had a significant degree of renal impairment. Sixty-one percent of the patients were being treated for congestive heart failure (CHF), and the remainder for atrial fibrillation with or without CHF. Overall, 67 percent of the serum digoxin assays were judged to be appropriate, particularly those requested for evaluation of possible digitalis toxicity or the dosage in renal impairment, but only 43 percent of the assays used to assess maintenance therapy or the patient's compliance were deemed appropriate. A significant difference was found in the percentage of appropriate assays useful by the physicians, as compared to the percentage of inappropriate assays. Inappropriate serum digoxin assays cost about $30,000 annually in this 680-bed hospital. Stricter criteria for admission assays would eliminate much of this excessive usage.