Unexplained increase in serum digoxin: a case report.

We describe a patient with unexpectedly high serum digoxin after cardiac surgery. To control atrial fibrillation in the immediate postoperative period, she was given a brief trial of digoxin (four 0.25-mg doses) over 12 h. Serum digoxin 6 h later was 2.5 micrograms/L. Two days later, the patient developed ventricular fibrillation, which progressed to cardiac arrest. During or immediately after resuscitation, blood was drawn for a digoxin measurement, and the concentration reported was 9.3 micrograms/L; this result was verified by repeated analysis. Digoxin decreased rapidly and progressively to near 4.0 micrograms/L over the next several hours and thereafter decreased slowly to 1.0 microgram/L over the next 11 days, despite no digoxin being administered. The unexpectedly high digoxin raised questions about the accuracy of the digoxin measurement, particularly about the possible influence of the digoxin-like immunoreactive factor. Analytical approaches to distinguishing true digoxin from this factor and other artifacts of digoxin measurement were applied to this patient, with unanticipated results.