Some factors affecting a commercial kit for radioimmunoassay of digoxin using tritiated digoxin

Some factors affecting results of digoxin determinations using one commercially available radioimmunoassay kit are described and discussed. Serum of pregnant women, cord blood, amniotic fluid and serum of patients taking spironolactone may show erroneously high digoxin activity due to lack of specificity of the antiserum. Cross-reaction with digitoxin was found to vary substantially with antibody-lot. Haemaccel (5 g/1) in the sample leads to too low results. When ethanol (100 g/1) is present results are too high. The need for testing the specifity of every new lot of antiserum before use is stressed.