title: Disposable-column radioimmunoassay for serum digoxin with less interference from metabolites and endogenous digitalis-like factors.
abstract: A preparative extraction step using disposable C18 low-pressure chromatography columns greatly improved the specificity of a commercially prepared digoxin radioimmunoassay (RIA). Elution solvents were isopropanol/water (15/85 by vol), which extracted most immunoreactive digitalis-like factors and metabolites, and methanol, which extracted digoxin for RIA. Many different digoxin RIA kits could be used. The coefficients of variation for replicates and duplicates were 4.6% and 5.2%. Analytical recoveries of digoxin standards in serum of 1.0, 0.5, and 0.1 microgram/L were 96%, 95%, and 88%, respectively. Serum digoxin was assayed by this method in 200 patients, 47 of whom were studied by HPLC-RIA. Values correlated better with "true digoxin" by HPLC-RIA (r = 0.93) than did values found by direct assay (r = 0.63). The mean for the isopropanol fraction as a percentage of the mean direct RIA value was higher for the 21 dialysis-dependent patients than was that found for the 179 nondialysis patients (P less than 0.004). The method is suggested as being most useful when metabolites or digitalis-like factors are known to be often high and values for digoxin are disproportionate to the dose.
authors.affiliation: General Hospital, St. John's, NF, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Longerich
authors.forename: S
authors.initials: S
authors.lastname: Vasdev
authors.forename: E
authors.initials: E
authors.lastname: Johnson
authors.forename: M H
authors.initials: MH
authors.lastname: Gault
mesh_terms: D000433:1-Propanol; D001798:Blood Proteins; D002298:Cardenolides; D002851:Chromatography, High Pressure Liquid; D004077:Digoxin / Q000097:blood*; D006801:Humans; D007668:Kidney / Q000502:physiology; D011863:Radioimmunoassay; D011933:Reagent Kits, Diagnostic; D012503:Saponins; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
chemical_list: D001798:Blood Proteins; D002298:Cardenolides; D011933:Reagent Kits, Diagnostic; D012503:Saponins; C034504:digoxin-like factors; D004077:Digoxin; D000433:1-Propanol; D000254:Sodium-Potassium-Exchanging ATPase