Test ID: FRT3P    
T3 (Triiodothyronine), Free and Total, Serum

The instrument used is a Beckman Coulter DXI 800. The access total and free triiodothyronine (T3) assays are competitive-binding immunoenzymatic assays. For the total T3 assay, sample is added to a reaction vessel with a stripping agent to dissociate T3 from the binding proteins. T3 in the sample competes with the T3 analogue coupled to biotin for anti-T3 alkaline Phosphatase conjugate. Of the resulting antigen:antibody complexes, the T3 analogue:antibody complexes are bound to the streptavidin-coated solid phase. Separation in a magnetic field and washing removes the sample T3:antibody complexes and other materials not bound to the solid phase.

For the Free T3 (FT3) assay, sample is added to a reaction vessel with mouse monoclonal antitriiodothyronine (anti-T3) and paramagnetic particles coated with goat antimouse capture antibody. During the first incubation, free T3 in the sample reacts with the anti-T3 antibody and is subsequently bound to the capture antibody. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field, while unbound materials are washed away. Next, T3-alkalinephosphatase conjugate and buffer are added to the reaction vessel to react with the remaining anti-T3 antibody binding sites. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field, while unbound materials are washed away. For both the total T3 and the FT3 assays, the chemiluminescent substrate Lumi-Phos* 530 is added to the vessel and light generated by the reaction is measured with a luminometer. The light production is inversely proportional to the concentration of total and FT3 in the sample. The amount of analyte in the sample is determined from a stored, multipoint calibration curve. (Package Insert: Beckman Coulter Ireland Inc. Ireland, 2005)

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