HomogeneousApoenzymeReactivationImmunoassayforThyroxin-Binding Globuhnin Serum

In this automated apoenzyme reactivation immunoassay system (Ames Optimate’”)forthyroxin-binding globulin (TBG),thesampleand M-aminohexylflavin adeninedinucleotide-labeled TBG reactsequentially withantiserum. Then apoglucose oxidaseis added to combine with the free fraction and generate glucose oxidase activity, which is measured colorimetrically. The assay requires 100 .tLof sample and covers the clinically significant range for TBG (<2.5 to 55 mg/L). The first result isobtainedin16 mm; assay of 29 samples and their blanks is completed in <1 h. The lower limit of detection is about 2.5 mg/L. Betweenassay CV5 (n = 9) were <9%, within-assayCVs (n = 5)were <6%, and analytical recoveryofTBG was 103-112%. Reagents are stable at 4 #{176}C for at least five months. Results by this method for serum TBG (y) compared well with those determinedby radioimmunoassay(): y = 1.029x 0.352(r = 0.990,n = 49,S = 1.165mg/L).Inaddition, with39other seratheratio oftotal thyroxin (byRIA)toTBG comparedwell withfreethyroxinmeasured by equilibrium dialysis (r = 0.930) and the free thyroxin index (r = 0.970).