Monitoring digoxin therapy: The use of plasma digoxin concentration measurements in the diagnosis of digoxin toxicity

The usefulness of measuring plasma digoxin concentrations in the diagnosis of digoxin toxicity has been assessed in 83 in-patients. the mean plasma digoxin concentration in clinically toxic patients was significantly higher than the mean concentration in non-toxic patients. the overlap between the groups, however, was extensive and could partly be accounted for by hypokalaemia in those toxic patients whose plasma digoxin concentration was less than 3 ng/ml. there was, in addition, a higher incidence of hyperkalemia, without obvious cause, in toxic patients than in non-toxic patients. consideration of the incidence of various non-cardiac factors, specifically plasma potassium concentration > 5.0 mmol/1, plasma creatinine concentration > 150 µmol/1, daily maintenance dose > 6 µg/kg, and age > 60 years, led to the development of guidelines to aid in the diagnosis of digoxin toxicity. patients with plasma digoxin concentration > 3 ng/ml or with hypokalaemia should be considered probably toxic and those with plasma digoxin concentration ≤ 3 ng/ml in the absence of hypokalaemia should only be considered toxic if they have at least two of the non-cardiac factors outlined above. plasma digoxin concentrations could not be predicted with more than 31 per cent certainty by considering the magnitude of those non-cardiac factors. © 1978, Oxford University Press.