title: Free thyroxine solid-analog immunoassays. investigation of the albumin effect on the antibody binding to immobilized thyroxine-protein conjugates.
abstract: A reliable one-step, analog-based FT4 immunoassay should be characterized by minimal binding of the serum thyroxine-binding proteins to thyroxine-analogs, used either as liquid-phase tracers or as solid-phase reagents. In this work, we investigated the effect of serum albumin concentration on the anti-T4 antibody binding to immobilized T4-protein conjugates with respect to the molecular weight (MW) and the T4-to-protein molar ratio of the conjugates. It was found that the presence of albumin in the serum sample, at concentrations up to 120 g/L, slightly decreased the antibody binding to the immobilized conjugates (less than 10%). In addition, this decrease was independent of both the MW and the T4-to-protein molar ratio of the conjugates. On the other hand, using the same conjugates as liquid-phase labeled analogs, the observed decrease ranged between 2 and 33%, depending on the MW of the conjugate. These findings indicate that the use of immobilized T4-protein conjugates may improve FT4 immunoassay reliability, concerning, especially, the issues of serum albumin concentration and/or affinity alterations.
authors.affiliation: Immunoassay Laboratory, I/R-RP, NCSR Demokritos, Aghia Paraskevi, Athens, Greece.
authors.forename: Anastasia D
authors.initials: AD
authors.lastname: Zacharopoulou
authors.forename: Ion
authors.initials: I
authors.lastname: Christofidis
authors.forename: Sotiris E
authors.initials: SE
authors.lastname: Kakabakos
authors.forename: Michael A
authors.initials: MA
authors.lastname: Koupparis
mesh_terms: D006801:Humans; D007118:Immunoassay / Q000379:methods*; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism*; D013974:Thyroxine / Q000032:analysis* / Q000378:metabolism
chemical_list: D012709:Serum Albumin; D013974:Thyroxine