Test Catalog

Test ID: T4BPE    
Thyroxine-Binding Protein Electrophoresis, Serum

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



Adult (> or =20 years): 4.5-11.7 mcg/dL


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

Interpretation Provides information to assist in interpretation of the test results

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

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.


Some patients who have been exposed to animal antigens, either in the environment or as part of treatment or imaging procedure, may have circulating anti-animal antibodies present. These antibodies may interfere with the T4 assay reagents to produce unreliable results.

Clinical Reference Recommendations for 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

3. Mimoto MS, Refetoff S: Clinical recognition and evaluation of patients with inherited serum thyroid hormone-binding protein mutations. J Endocrinol Invest. 2020 Jan;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 Oct;29(5):735-747