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Interpretive Handbook

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Test 8838:
Thyroxine-Binding Protein Electrophoresis, Serum

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

Normally, almost all (99.5%) thyroxine 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.

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 clinical condition of a patient.

 

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.

 

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

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 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%)

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.

THYROXINE-BINDING PROTEIN ELECTROPHORESIS

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

Other protein binders: normally not present

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

 

THYROXINE, TOTAL

> or =12 months: 5.0-12.5 mcg/dL

Reference values have not been established for patients that are <12 months of age.

Clinical References 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