[Determination of digoxin in serum. Comparison of radioimmunoassay and a heterogeneous enzyme immunoassay (author's transl)].

This paper describes the evaluation of a heterogeneous enzymeimmunoassay (EIA, subtype ELISA) for the determination of digoxin in serum. Results are compared with those obtained from a radioimmunoassay (New England Nuclear, 125I-Digoxin). The limit of detection is 0.3 microgram/1 (0.4 nmol/1). The range of the test is from 0.3 unto 5.0 microgram/1 (0.4--6.4 nmol/1). Within-batch precision ranged from 7 to 11%, between-batch precision from 8--14%. Pure digoxin, added to solutions of albumin and pooled sera, gave recoveries between 87 and 106%. 116 sera from patients taking digoxin exclusively yielded no systematic difference compared to the results of a radioimmunoassay (RIA) (equation of the bivariate regression CELISA = 0.954 . CRIA + 0.14 (microgram/1) (0.18 nmol/1). Nevertheless marked differences between both tests were observed in individual cases. Digitoxin yielded in vitro and in vivo a cross-reactivity of 7 to 14% depending upon the concentration. In 68 sera from patients, taking digoxin plus spironolactone, we found results that were on average 0.48 microgram/1 (0.64 nmol/1) higher with the ELISA than with the RIA (p less than 0.01%). With respect to practicability the ELISA test for digoxin is very similar to the analogous RIA both using the solid phase technique.