Thyroxine-Binding Protein Electrophoresis, Serum
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
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.
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.
> or =12 months: 5.0-12.5 mcg/dL
Reference values have not been established for patients that are <12 months of age.
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%)
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
No significant cautionary statements
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