Test Catalog

Test ID: FRT4D    
T4 (Thyroxine), Free, Dialysis, Serum

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

The equilibrium dialysis method separates free thyroxine (FT4) from serum proteins and, thereby, also from protein-bound thyroxine (T4), before measuring it in the protein-free dialysate using sensitive, tandem mass spectrometry. The results are independent of the concentrations of the T4-binding proteins and unaffected by the presence of molecular variants of these proteins.(Soldin SJ, Soukhova N, Janicic N, et al: The measurement of free thyroxine by isotope dilution tandem mass spectrometry. Clin Chim Acta 2005 Aug;358:113-118; Masika LS, Zhao Z, Soldin SJ: Is measurement of TT3 by immunoassay reliable at low concentrations? A comparison of the Roche cobas 6000 vs. LC-MSMS. Clin Biochem. 2016;49[12]:846-849)

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, Wednesday, Thursday; 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.

3 days

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

8 days

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

2 weeks

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