digoxin and Liver-Failure

We examined the specificity of three automated digoxin immunoassays (Abbott TDxFLx Digoxin II assay, Baxter-Dade Stratus II Digoxin assay, and Ciba Corning ACS Digoxin assay) applied without modification to (a) sera from 229 digoxin-free patients in 12 cohorts associated with nonspecific or endogenous digoxin-like immunoreactive factor (DLIF) interference, and (b) drug-free serum supplemented with the major metabolites and analogs of digoxin. We observed three patterns of apparent digoxin results among the DLIF samples: one common to kidney and liver failure patients, where TDx and Stratus assays showed significant positive results; one common to newborns and cord blood, where only the TDx assay had significant interference; and one from cardiac surgery patients, where the Stratus assay alone showed interference. Of the three assays, the ACS had the least interference from DLIF. The assays also behaved differently with respect to cross-reactivity with digoxin metabolites, digitoxin, and digitoxin metabolites. The ACS assay again had the least analog or metabolite cross-reactivity. The three methods agreed well on digoxin-positive specimens, with a mean bias of <0.15 microgram/L digoxin for each and discrepancies (defined as >3 SD between the assay pairs compared) of only 3-5%.

Topics: Antibody Specificity; Autoanalysis; Blood Proteins; Cardenolides; Cohort Studies; Digoxin; Fetal Blood; Humans; Immunoassay; Infant, Newborn; Liver Failure; Reagent Kits, Diagnostic; Renal Insufficiency; Saponins; Sensitivity and Specificity

We have evaluated the new Roche digoxin "On Line" procedure for use in a pediatric population with particular interest in the potential for interference by digoxin-like immunoreactive factor (DLIF). An initial study comparing digoxin values obtained with the new Roche procedure with determinations on an Abbott TDx, American Dade Stratus, and COBAS-FARA using Microgenics Cedia reagents, found good correlations with these established methods. The Roche method was suitably precise and utilized either serum or plasma. Interference by DLIF was assessed by analyzing specimens from patients not receiving digoxin but likely to contain DLIF, with the argument that non-zero values represent cross-reactivity of anti-digoxin antibodies with DLIF endogenous to these specimens. When specimens from neonates, women with second/third trimester pregnancies, and patients with renal and liver failure were assayed with the Roche, Stratus, and TDx methods, all three methods measured DLIF in some specimens, but the Roche method possessed the lowest overall DLIF interference. The modest extent of DLIF interference and the requirement of a small amount of specimen make the Roche method superior in monitoring digoxin in a pediatric population.

Topics: Digoxin; Drug Monitoring; Humans; Immunoassay; Infant, Newborn; Kinetics; Liver Failure; Renal Insufficiency