Iodine-125--digoxin radioimmunoassay: comparison of commercial kits

Iodine-125-digoxin radioimmunoassay kits available from Abbott Diagnostics (AD), Dade Division (D), Schwarz/Mann (SM), and Clinical Assays (CA) were evaluated with respect to assay quality. The kit accuracies did not differ significantly at 2.0 ng/ml and the interassay coefficients of variation ranged from 9 percent (AD) to 21.4 percent (CA). The accuracy for all kits above 4 ng/ml is questionable, and since serum-dilution values correlated well with undiluted serum values, the dilution method of dose quantitation is preferable for levels above 4 ng/ml. Although all the kits were adequate for evaluating digoxin at the 2 ng/ml level, the Abbott kit seems to be of slightly better quality