Sorted By Test Name - Mayo Medical Laboratories

TIAG
82524
Clinical Information: 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: 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: 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:
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 95% absorbed, with oral bioavailability of about 90%. Tiagabine pharmacokinetics are linear over the
typical dose range of 2 to 24 mg. Steady-state is achieved within 2 days. Tiagabine is 96% bound to
human plasma proteins, mainly to serum albumin and alpha-1-acid glycoprotein. Co-administration with
valproate reduces protein binding to 94%, increasing the free fraction of tiagabine by 40%.(3,6) Based on
in vitro data, tiagabine is likely to be metabolized by the 3A isoform subfamily of hepatic cytochrome
P450 (CYP 3A), although contributions to the metabolism from CYP 1A2, CYP 2D06, or CYP 2C19
have not been excluded.(3)
Current as of January 4, 2013 7:15 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 1751