T3 uptake

Alphabetical Test listing

T3 uptake-994

T3 uptake
Thyroid Hormone-binding Ratio (THBR)
  • Thyroid function test for the diagnosis of hypothyroidism or hyperthyroidism, used with thyroxine (T4) or equivalent to provide free T4 index, FTI.
  • An indirect measure of binding protein, the T3 uptake reflects available binding sites (ie, reflects TBG).
  • T3 uptake is not a measurement of serum T3. It should never be used alone; rather, its usual application is use with thyroxine (T4).

This test reflects assessment of thyroxine-binding globulin (TBG) and should not be ordered alone.


Biotin supplements may interfere with assay.

It is recommended that patients abstain from any biotin containing supplement for 12 - 24 hours prior to blood draw. Biotin is commonly found in hair, skin and nail supplements and multivitamins.

1.0 mL
0.8 (pediatric)
0.7 mL
0.3 (pediatric)

Immediatley following collection, mix sample by gently inverting 5 times

  1. Allow sample to clot for a minimum of 30 minutes
  2. Spin within two (2) hours of sample collection

Gold serum separator (SST) tube

Lithium heparin (Li hep) plasma

Lt green plasma separator (PST):

Immediately following collection, mix sample thoroughly by gentle inverting 8 - 10 times to prevent clotting



  1. Allow sample to clot
  2. Spin within two (2) hours of sample collection
  3. Transfer serum to a Transfer vial/tube with cap - 12mL (LabCorp), labelled as serum

Lt green plasma separator (PST): 

Spin within two (2) hours of sample collection


Transfer vial/tube with cap - 12mL (LabCorp)


Lt green plasma separator (PST)


Ambient (preferred) - 14 days

Refrigerated - 14 days

Frozen - 14 days

Freeze/thaw cycles: stable x3


LabCorp Burlington (001156): R-NX
1 - 3 days

Electrochemiluminescence Immunoassay (ECLIA)


An interpretive report will be provided

Biotin interference - see Patient preparation