Test Catalog

Test ID: T4BPE    
Thyroxine-Binding Protein Electrophoresis, Serum

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

Thyroxine-binding protein electrophoresis:

Radioactive (125)I-thyroxine (T4) is incubated with patient serum, the mixture is electrophoresed on polyacrylamide gel, and the profile of binding proteins is quantitated by counting the radioactivity in slices of the gel. The binding proteins are separated by both charge and size with prealbumin on the anode side followed by albumin and thyroxine-binding globulin (TBG). Gamma globulin remains at the origin, and free T4 migrates between albumin and prealbumin. The concentration of (125)I-T4 added will saturate TBG but not the other T4-binders. The binding is expressed as thyroxine-binding capacity at 100 mcg T4/dL serum.(Unpublished Mayo method).



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. This signal is measured against a calibration curve to determine patient results.(Package insert: Elecsys T4. Roche Diagnostics; V 2.0 English 03/2020)

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.

Once per month

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.

2 days

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

29 days

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

90 days

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