title: A critical appraisal of a further three new commercial digoxin radioimmunoassay kits with reference to cross-reacting substances.
abstract: A further 3 digoxin radioimmunoassay (RIA) kits have been evaluated for performance and cross-reaction with digitoxin, spironolactone, canrenone and furosemide (Lasix-Hoechst). Effects of serum protein concentrations have also been tested. The kits tested were from the following manufacturers: A) Diagnostic Products Corporation Digoxin RIA Kit. B) Byk-Mallinckrodt SPAC Digoxin Kit. C) Boehringer-Mannheim Digoxin RIA Kit. All kits used a 125I-labelled tracer. Kit A used a conventional liquid phase system using double-antibody separation for bound and free drug, Kits B and C used a solid-phase antibody coated tube method. All kits showed a lower cross-reaction to digitoxin than quoted by the manufacturer. Cross-reaction to spironolactone (Aldactone--Boehringer-Mannheim) was less than 1.50 nmol/l at a serum concentration of 125 mg/l Aldactone in all 3 kits. The cross-reaction to canrenone was somewhat higher, 5.2 nmol/l "digoxin" being measured in one kit at a serum canrenone concentration of 125 mg/l. There was no cross-reaction with furosemide in any kit, even at a serum concentration of 5 g/l. The coated-tube assays were affected by serum albumin and globulin concentration changes, one kit showing a difference of over 50% binding in the range 1--20% albumin. The double-antibody kit did not show dependence on the concentration of these proteins. All kits measured digoxin with good reproducibility in the range 0.40--10.0 nmol/l.
mesh_terms: D001798:Blood Proteins / Q000032:analysis; D002192:Canrenone / Q000097:blood; D003429:Cross Reactions; D004074:Digitoxin / Q000097:blood; D004077:Digoxin / Q000097:blood*; D005069:Evaluation Studies as Topic; D005665:Furosemide / Q000097:blood; D006801:Humans; D011863:Radioimmunoassay / Q000295:instrumentation; D011933:Reagent Kits, Diagnostic; D013148:Spironolactone / Q000097:blood
chemical_list: D001798:Blood Proteins; D011933:Reagent Kits, Diagnostic; D013148:Spironolactone; D004077:Digoxin; D002192:Canrenone; D005665:Furosemide; D004074:Digitoxin