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Test ID: TBPE    
Thyroxine-Binding Protein Electrophoresis, Serum

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Useful For Suggests clinical disorders or settings where the test may be helpful

Explaining unusual thyroxine (T4), free T4, and thyroxine-binding globulin (TBG) 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

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

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 Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


10.3-24.9 mcg T4/dL bound to TBG

11.5-34.1 mcg T4/dL bound to albumin

48.8-70.4 mcg T4/dL bound to prealbumin

Interpretation Provides information to assist in interpretation of the test results

Rare protein-binding abnormalities may be suspected in euthyroid patients having an elevated total thyroxine (T4) but normal thyroxine-binding globulin (TBG).


The following example is from a healthy 40-year-old male with familial dysalbuminemic hyperthyroxinemia, a benign familial condition that can be confused with hyperthyroidism:

-Increased T4 of 14.4 mcg/dL (normal=5.0-12.5 mcg/dL)

-Normal TBG of 20.1 mcg/dL (normal=12-26 mcg/mL)


The thyroxine-binding protein electrophoresis (TBPE) assay identified that of the saturating dose of (125)I-T4:

-52% was bound to albumin (normal 12%-34%)

-36% was bound to thyroxine-binding prealbumin (normal 49%-70%)

-13% was bound to TBG (normal 10%-25%)


In this example, based on the TBPE findings, this patient’s increased serum T4 was determined due to increased binding to albumin. This was suggestive of familial dysalbuminemic hyperthyroxinemia (FDH), an inherited abnormality characterized by the presence of a variant serum albumin with preferential affinity for T4.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

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


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.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

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

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