Mobile Site ›
Print Friendly View

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

‹ Back to Pediatric index

Method Description Describes how the test is performed and provides a method-specific reference

Triiodothyronine (T3) testing is performed on a Roche cobas instrument. The Roche triiodothyronine assay (T3) is a competitive assay using electrochemiluminescence detection. Bound T3 is released from binding proteins by 8-anilino-1-naphthalene sulfonic acid (ANS). The patient specimen is incubated with a sheep polyclonal anti-T3 antibody labeled with ruthenium. Streptavidin-coated microparticles and biotinylated T3 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 removed and application of a voltage to the electrode induces the electrochemiluminescent emission. This signal is measured against a calibration curve to determine patient results.(Package insert: Roche cobas. Roche Diagnostics, Indianapolis, IN. 2011).


For the free T3 (FT3) assay, testing is performed on the Beckman Coulter DxI 800. The Access Free T3 assay is a 2-step competitive-binding immunoenzymatic 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-alkaline phosphatase 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. 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, 2010)

PDF Report Indicates whether the report includes an additional document with charts, images or other enriched information


Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.

Monday through Friday; 3rd shift

Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.

1 day

Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result

3 days

Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

1 month

Performing Laboratory Location The location of the laboratory that performs the test

New England