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Mayo Clinic Laboratories

Test Code T4BPE Thyroxine-Binding Protein Electrophoresis, Serum

Useful For

Explaining unusual thyroxine (T4), free T4, and thyroxine-binding globulin test results that do not correlate with the patient's clinical presentation

Detecting the presence of aberrant thyroxine-binding proteins, such as abnormal forms of albumin and prealbumin

Detecting selective deficiency of one of the thyroxine-binding proteins

Detecting antibodies to T4

An adjunct to the diagnosis of patients with high T4 concentration due to peripheral hormone resistance by ruling out thyroxine-binding abnormalities

Profile Information

Test ID	Reporting Name	Available Separately	Always Performed
TBPE	Thyroxine-Binding Protein Electro	No	Yes
T4	T4 (Thyroxine), Total Only, S	Yes	Yes

Method Name

TBPE: Electrophoresis

T4: Electrochemiluminescence Immunoassay (ECLIA)

Reporting Name

Thyroxine-Binding Protein Electro

Specimen Type

Serum

Ordering Guidance

This assay measures thyroxine binding to various proteins.

For analysis of thyroxine-binding globulin, see TBGI / Thyroxine-Binding Globulin (TBG), Serum.

For immunologic assay of prealbumin, see PALB / Prealbumin, Serum.

This test should not be requested in patients who have recently received radioisotopes, therapeutically or diagnostically, because of potential assay interference. A recommended time period before collection cannot be made because it will depend on the isotope administered, the dose given, and the clearance rate in the individual patient.

The total thyroxine (T4) test should not be used in patients receiving treatment with lipid-lowering agents containing dextrothyroxine unless therapy is discontinued for 4 to 6 weeks to allow the T4 physiological state to become re-established prior to testing.

Specimen Required

Patient Preparation: For 12 hours before specimen collection, patient should not take multivitamins or dietary supplements (eg, hair, skin, and nail supplements) containing biotin (vitamin B7).

Supplies: Sarstedt Aliquot Tube, 5 mL (T914)

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1.6 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.

Specimen Minimum Volume

0.8 mL

Specimen Stability Information

Specimen Type	Temperature	Time
Serum	Refrigerated (preferred)	7 days
	Frozen	30 days
	Ambient	24 hours

Reject Due To

Gross hemolysis	Reject
Gross lipemia	Reject
Gross icterus	Reject

Clinical Information

Normally, almost all thyroxine (99.5%) is bound to thyroxine-binding globulin, prealbumin, and albumin. Deficiencies and aberrant forms of these binding proteins can occur, causing difficulties interpreting thyroid function test results. Such abnormalities may be identified by thyroxine-binding protein electrophoresis.

Reference Values

THYROXINE-BINDING PROTEIN ELECTROPHORESIS:

10.3-24.9 mcg T4/dL bound to thyroxine-binding globulin

11.5-34.1 mcg T4/dL bound to albumin

48.8-70.4 mcg T4/dL bound to prealbumin

T4 (THYROXINE), TOTAL ONLY:

Pediatric:

0-5 days: 5.0-18.5 mcg/dL

6 days-2 months: 5.4-17.0 mcg/dL

3-11 months: 5.7-16.0 mcg/dL

1-5 years: 6.0-14.7 mcg/dL

6-10 years: 6.0-13.8 mcg/dL

11-19 years: 5.9-13.2 mcg/dL

Adult (≥20 years): 4.5-11.7 mcg/dL

For SI unit Reference Values, see www.mayocliniclabs.com/order-tests/si-unit-conversion.html

Interpretation

An interpretive comment will be provided based on the total thyroxine concentration and the thyroxine-binding protein profile observed in the electrophoresis.

Cautions

Thyroxine-binding globulin values may be elevated in women taking estrogens and during pregnancy.

In rare cases, some individuals can develop antibodies to mouse or other animal antibodies (often referred to as human anti-mouse antibodies [HAMA] or heterophile antibodies), which may cause interference in some immunoassays. Caution should be used in interpretation of results and the laboratory should be alerted if the result does not correlate with the clinical presentation.

Clinical Reference

1. Hay ID, Klee GG. Thyroid dysfunction. Endocrinol Metab Clin North Am. 1988;17(3):473-509

2. Bartalena L, Robbins J. Thyroid hormone transport proteins. Clin Lab Med. 1993;13(3):583-598

3. Mimoto MS, Refetoff S. Clinical recognition and evaluation of patients with inherited serum thyroid hormone-binding protein mutations. J Endocrinol Invest. 2020;43(1):31-41. doi:10.1007/s40618-019-01084-9

4. Pappa T, Ferrara AM, Refetoff S. Inherited defects of thyroxine-binding proteins. Best Pract Res Clin Endocrinol Metab. 2015;29(5):735-747

Method Description

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).

Thyroxine:

The Roche T4 (thyroxine) assay is a competitive assay using electrochemiluminescence detection. Bound T4 is released from binding proteins by 8-anilino-1-naphthalene sulfonic acid. 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)

Day(s) Performed

Fourth Friday of the month

Report Available

29 to 35 days

Specimen Retention Time

90 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information

84436

82664

LOINC Code Information

Test ID	Test Order Name	Order LOINC Value
T4BPE	Thyroxine-Binding Protein Electro	48073-1

Result ID	Test Result Name	Result LOINC Value
2860	TBG	14016-0
2861	Albumin	11062-7
T4	T4 (Thyroxine), Total Only, S	83119-8
2862	Pre-Albumin	14014-5
2863	Abnormal Binding Protein	48767-8
3345	Comment	50681-6

Secondary ID

38507

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