A commercial digoxin radioassay modified for use as an emergency ("stat") procedure

A recent "stat" procedure recommended by the manufacturer for use with a commercial digoxin radioassay involves doubling the amount of antibody used in the regular procedure, to compensate for the decrease in binding that results from use of a shorter (10 min) incubation. This has two obvious disadvantages: increased material cost and decreased sensitivity because of the increase in the binding capacity of the assay. In our modified procedure, we kept the binding capacity constant by decreasing the volume of the incubation mixture without increasing the amount of antibody. Total binding and the rate of binding on 10-min incubation are 50.4 and less than 1.3% per minute, respectively. Results by our modified stat procedure compare well with those by the manufacturer's suggested regular procedure in terms of sensitivity, accuracy, and precision, and are more sensitive and economical than those by the manufacturer's suggested stat procedure.