Endogenous digoxin-like immunoreactive factors (DLIF) as measured by the CEDIA digoxin assay and a fluorescence polarization immunoassay.

The sensitivity of a new homogeneous enzyme immunoassay for the determination of digoxin (CEDIA Digoxin assay) and a fluorescence polarization immunoassay (FPIA) to interference by digoxin-like immunoreactive factors (DLIF) was studied in sera from pregnant women, newborns, patients undergoing hemodialysis and patients with renal insufficiency, but without hemodialysis. None of the patients had been treated with digoxin or digitoxin. Cross-reactivity of DLIF in the CEDIA assay was generally lower than in the FPIA. Data on the distribution DLIF of values and method comparisons showed that sera of the four patient groups reacted in a completely different way in both assays, suggesting that the nature of DLIF in the four groups is not identical. Addition of digoxin to sera of patients not treated with this drug resulted in a reduction of the apparent DLIF concentration in the CEDIA assay and the FPIA. This shows that DLIF interference may be less pronounced in sera of patients undergoing digoxin therapy compared to untreated persons. Although the CEDIA assay is less sensitive to DLIF interference than the FPIA, further efforts are needed to reduce the extent of this interference.