Specificity of the digoxin radioimmunoassay with respect to dihydrodigoxin

An investigation was conducted to determine the specificity of the digoxin antibody provided in a commercially available radioimmunoassay kit with respect to dihydrodigoxin. Over the concentration range of 0.5 to 8.0 ng./ml. dihydrodigoxin displaced the 125I digoxin derivative from the antibody to a degree that could be significant at clinically observed serum and urine digoxin concentrations.