Red blood cell electrolytes for monitoring digoxin therapy in adults

Red blood cell (RBC) electrolyte concentrations were determined, with a method that can be applied easily in any clinical chemistry laboratory, in 18 patients not on digoxin therapy and 37 patients on maintenance digoxin therapy for various diagnoses. Of the digoxin-treated patients, 11 had electrocardiographic changes and other clinical evidence of digoxin toxicity. Mean RBC sodium was higher and mean RBC potassium was lower in patients on prolonged digoxin therapy than in controls, and these changes were more pronounced in patients with toxic symptoms. In the group of 11 patients with toxicity, a positive correlation was found between the ratio of RBC sodium to potassium and plasma digoxin levels (r = 0.8234, p less than 0.05). Plasma digoxin concentrations did not clearly distinguish between toxic and nontoxic patients. The RBC sodium/potassium ratio, however, identified 35 of 37 patients correctly, with two patients from the toxic and two patients from the nontoxic group giving the same results. Changes in intracellular erythrocyte electrolytes in adults appear to correlate closely with clinical signs of digoxin toxicity.