Enzyme-Multiplied Immunoassay (EMIT 2000) Digoxin Assay Compared with Fluorescence Polarization Immunoassay and Amerlex 125I-Radioimmunoassay at Two Australian Centers

Digoxin assays in plasma from patients treated with the drug have played an integral role in its therapeutic management. Commercial digoxin immunoassays have been criticized for poor performance owing to various interferences and limited sensitivity. The present study compared the performance of a new enzyme-multiplied immunoassay technique (EMIT 2000) to fluorescence polarization immunoassay (FPIA) and radioimmunoassay (RIA) in two separate Australian centers. Comparisons were made using standard indices of precision and accuracy, samples taken from patients, quality-assurance samples, and cord blood samples from neonates, in which high concentrations of digoxin-like immunoreactive substances (DLIS) would be anticipated. The results confirmed satisfactory precision and accuracy for therapeutic drug monitoring purposes, a sensitivity of < 0.1 microgram/L, and very low DLIS interference, as assessed by assay of neonatal cord blood samples.