Thyroxine Binding Globulin

Cleveland HeartLab T, Test

CPT Code: 84442
Order Code: C2378
ABN Requirement: No
Synonyms: TBG
Specimen: Serum
Volume:  0.5 mL
Minimum Volume:  0.4 mL
Container: Gel-barrier tube (SST, Tiger Top)



  1. Collect and label sample according to standard protocols.
  2. Gently invert tube 5 times immediately after draw. DO NOT SHAKE.
  3. Let tube stand in a vertical position to allow blood to clot 30 minutes.
  4. Centrifuge at 1300 rcf for 10 minutes at room temperature.

Transport: Store serum at 2-8°C after collection and ship the same day per packaging instructions provided with the Cleveland HeartLab, Inc. shipping box.


Ambient (15-25°C): 24 hours
Refrigerated (2-8°C):
7 days
Frozen (-20°C):
30 days
Deep Frozen (-70°C):
30 days

Causes for Rejection: Specimens other than serum; improper labeling; samples not stored properly; samples older than stability limits

Methodology: Chemiluminescence Immunoassay (CLIA)

Turn Around Time: 3-6 days

Reference Range:

Age ug/mL
All Ages 13-30


Clinical Information: Determine binding capacity for T4; document cases of hereditary deficiency of TBG, in work-up of thyroid disease, particularly in patients with low T4, high T3 (uptake) who clinically seem eumetabolic. Such patients may have hereditary anomalies of TBG. They may require no treatment.