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

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

This is a chemiluminometric immunoassay. T-Uptake (TU) is measured using an automated sandwich two-site chemiluminometric immunoassay on the Advia: Centaur instrument. The specimen is incubated with acridinium ester (AE)-labeled triiodothyronine (T3)-BGG (bovine gamma globulin) and unlabeled triiodothyronine (T3). The unlabeled T3 fills available thyroid-binding sites in the specimen; and the AE-labeled T3-BGG does not bind to the binding proteins in the specimen. The AE-labeled T3-BGG and the remaining unlabeled T3 then compete for binding sites on a monoclonal mouse anti-T3 antibody in the solid phase. A greater amount of unlabeled T3 bound to the binding proteins in the specimen results in more T3-BGG-AE binding to the monoclonal antibody, an indication of a greater amount of unsaturated binding proteins. A direct relationship exists between the concentration of unsaturated binding proteins in a specimen and the relative light units (RLU’s) detected by the system.(Package insert: Bayer Advia: Centaur TUP. Bayer Diagnostics, East Walpole, MA 02032)

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, Sunday; 6 a.m.-3 p.m.

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.

Same day/1 day

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

2 days

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

7 days

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