A study of the CEDIA digoxin immunoassay.

We evaluated the CEDIA digoxin immunoassay (Microgenics, Inc., Concord, CA), as performed with the Cobas-Bio centrifugal analyzer. In assays of sera with known concentrations of digoxin, the enzyme activity, measured when two beta-galactosidase (EC 3.2.1.23) fragments were combined according to the assay format, was proportional to the digoxin concentration. Results of assays of sera containing 0 to 3 micrograms of digoxin per liter correlated well when compared with an RIA method: CEDIA, microgram/L = 1.00 x RIA - 0.06 microgram/L (n = 90, r = 0.95, Sxy = 0.05). Duplicate assays of three control sera containing 0.8, 2.2, or 3.3 micrograms/L, each analyzed 20 times a day with each group of patients' samples, gave within-run CVs of 1-3% and day-to-day CVs of 3-12%. The reconstituted CEDIA reagents were stable for at least a month at 5 degrees C. As many as 25 samples and controls can be assayed in half the time needed to complete a similar number of RIA measurements with comparable results.