title: Effect of protein concentration on the determination of digoxin in serum by fluorescence polarization immunoassay.
abstract: Determination of digoxin by fluorescence polarization immunoassay (FPIA) with the Abbott "TDx" is significantly influenced by the concentration of total serum protein. Each 10 g/L increase in serum protein results in an 8% decrease in measured digoxin. Studies with [3H]digoxin confirmed that digoxin binds to the protein pellet during the trichloroacetic acid precipitation step before the immunoassay. Serum protein, or equal concentrations of albumin or gamma-globulin, exert an equivalent effect on the apparent digoxin value. Because the total protein concentration of the assay calibrators is low (50 g/L) compared with its reference interval in serum (60-80 g/L), results by FPIA may be expected to be low by an average of 16% (range, 8-24%). Digoxin results by FPIA will be most nearly accurate when the calibrators include a total protein concentration of about 70 g/L. Patients' specimens with abnormally high or low protein content will give falsely high or low results for digoxin.
mesh_terms: D001798:Blood Proteins / Q000032:analysis; D004077:Digoxin / Q000097:blood*; D005454:Fluorescence Polarization; D006801:Humans; D007118:Immunoassay / Q000379:methods; D011485:Protein Binding; D011863:Radioimmunoassay; D011933:Reagent Kits, Diagnostic; D012709:Serum Albumin / Q000032:analysis; D014238:Trichloroacetic Acid; D005719:gamma-Globulins / Q000032:analysis
chemical_list: D001798:Blood Proteins; D011933:Reagent Kits, Diagnostic; D012709:Serum Albumin; D005719:gamma-Globulins; D014238:Trichloroacetic Acid; D004077:Digoxin