Alternative Names
  • T4-Uptake
  • T-Uptake
  • Thyroxine Binding Capacity-TBC
  • Thyroxine Binding Index-TBI
  • Testosterone-Estradiol Binding Globulin
  • Testosterone-binding Globulin

Test Code: 4022

CPT: 84479
Tests Included T-Update
Use Used to asses the thyroxine-binding capacity of unsaturated proteins in serum and plasma and may also be used in conjunction with a total thyroxine measurement to provide a calculated free thyroxine index (FTI).
Clinical Utility In hypothyroidism the relatively unsaturated binding proteins reflect a decreased thyroid uptake value. In hyperthyroidism the thyroid uptake value increases due to the highly saturated binding proteins
Intended Patient Population 18+ and Older Adult Males & Females
Patient Preparation None Specified
Sample Serum, Plasma
Tube Red, Green, Tiger
Volume 4mL Whole Blood (1mL Serum/Plasma)
Min Sample Volume 0.5 mLs
Reference Ranges NEED TO FIND OUT
Analytical Measurement Range N/A
Units %
Test Methodology Chemiluminescent Immunoassay
Test Turnaround Time 2 Days
Limitations In addition to thyrometabolic disorders, the following can alter the thyroid uptake value in euthyroid individuals:1,2

Increased Thyroid Uptake: Reduced TBG synthesis (androgens or anabolic steroids), Hypoproteinemia (nephrosis, malnutrition), Drugs (Phenytoin, salicylates), Extrathyroidal disease (hepatic disease, generalized illness, acromegaly), and Hereditary TBG deficiency.

Decreased Thyroid Uptake: Increased TBG synthesis (pregnancy, estrogen administration, oral contraceptives), Hyperproteinemia, Drugs (prolonged phenothianzine administration), Extrathroidal disease (hepatic disease), Hereditary TBG excess.
Shipping Requirements Refrigerated
Specimen Stability 7 Days RF
Reject Criteria Gross Hemolysis
Laboratory Developed Test (LDT) Yes
CMS Guidance NCD 190.22
  1. Gornall, AG, Luxton, AW, Bhavnani, BR. Endocrine disorders. In Applied Biochemistry of Clinical Disorders, 1986; 305-318. Edited by Gornall, A.G. Philadelphia, PA: J. B. Lippincott Co.
  2. White, GH. Recent advances in routine thyroid function testing. CRC - Critical Reviews in Clinical Laboratory Sciences, 1987, 24: 315-362.

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