Test ID: FRTUP    
Free Thyroxine Index (FTI), Serum

Thyroxine Binding Capacity:

Testing is performed on Roche Cobas e immunoassay analyzer. Thyroxine (T4) occupies the free binding sites in the serum sample. After addition of a T4-specific antibody labeled with a ruthenium complexa, the T4-polyhapten and the antibody derivative react to form a complex, the concentration of which is inversely proportional to the concentration of the excess, exogenous T4. This immunological complex becomes bound to the added streptavidin-coated microparticles via interaction of biotin and streptavidin.Application of a voltage to the electrode then induces chemiluminescent emission which is measured by a photomultiplier.(Package insert: Roche T-Uptake reagent, 2011-11. V18, Indianapolis, IN)

Thyroxine, Total:

Testing is performed on a Roche Cobas e immunoassay analyzer. The Roche T4 assay is a competitive assay using electrochemiluminescence detection. Bound T4 is released from binding proteins by 8-anilino-1-naphthalene sulfonic acid (ANS). Patient specimen is incubated with sheep polyclonal anti-T4 antibody labeled with ruthenium. Streptavidin-coated microparticles and biotinylated T4 are added for a second incubation during which the still free binding sites of the labeled antibody become occupied. The resulting immunocomplex becomes bound to the solid phase by interaction of biotin and streptavidin. The reaction mixture is aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. Unbound substances are then removed and application of a voltage to the electrode induces the electrochemiluminescent emission.(Package insert: Roche T4 reagent, 2011-06, V3, Indianapolis, IN)

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