Serum digoxin level - determined or estimated?

In 108 patients on maintenance digoxin therapy the serum digoxin levels were determined by means of homogeneous enzymoimmunoanalysis and compared with those estimated by means of a commonly accepted nomogram and with those estimated by means of the equation derived from multiple regression analysis of variables. By using stepwise discriminant analysis and a jacknifed classification matrix, based on serum digoxin and potassium levels, 96% and 90% of the classification of patients with and without clinical signs of digoxin intoxication, respectively, was correct. Based on serum creatinine and potassium levels and the daily digoxin dose/kg only 83% and 78% of the classification, respectively, was correct. The direct determination of serum digoxin level provides, in real time, information of higher reliability than does the estimate of the serum digoxin level. It is of basic importance in patients with dysrhythmias, in persons with an implanted pacemaker and in persons in whom the estimated levels of serum digoxin are around 2.6 nmol/l.