Improved micro-radioimmunoassay of digoxin in serum, with use of 125I-labeled digoxin.

A micro-radioimmunoassay of 125I-labeled digoxin is described in which 10-mul rather than 50-mul aliquots of sera are required. The method is a modification of a simplified, rapid, and accurate procedure, which is commercially available as a kit. There is excellent correlation between results by these two methods, in which lyophilized digoxin standards and insoluble antibody polymer are used. The digoxin concentration in capillary sera was not significantly different from that in the corresponding venous blood. It is clinically useful to monitor digoxin therapy in capillary sera, particularly in patients in whom blood sampling by venipuncture is inconvenient or difficult.