Using a commercially available digoxin radio-immunoassay kit, an accuracy of the order of ±10 per cent has been achieved. Precision could be improved by increasing the ratio (volume of plasma/volume of radioactive digoxin). The assay permitted separation of clinically toxic and non-toxic patients with plasma digoxin values of 3.5±0.6 (S.D.) ng. per ml. and 1.4±0.6 ng. per ml. respectively (p <0.001). A correlation between blood urea and plasma digoxin concentration was demonstrated (r=0.57, p <0.001).
The assay was particularly useful in the confirmation and follow-up of suspected digoxin poisoning in attempted suicide, and in renal failure to arrive at a modified digoxin dosage schedule.
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