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Paediatric Laboratory Medicine

T3 - Total, Blood

Clinical Significance

3,5,3’ Triiodothyronine (T3) is a thyroid hormone with a molecular weight of 651 daltons and a half-life in serum of 1.5 days. T3 circulates in the blood as an equilibrium mixture of free and protein bound hormone. T3 is bound to thyroxine binding globulin (TBG), prealbumin, and albumin It has become apparent in recent years that T3 plays an important role in the maintenance of the euthyroid state. Serum T3 measurements can be a valuable component of a thyroid screening panel in diagnosing certain disorders of thyroid function as well as conditions caused by iodine deficiency. Clinically, measurements of serum T3 concentration are especially valuable in diagnosing hyperthyroidism and in following the course of therapy for this disorder.

Test Name

T3 - Total, Blood

Test Code



Biochemistry - Biochemistry


Abbott Ci4100

External Proficiency Testing


Turn Around Time

Monday to Friday

Specimen Type

Serum, Sodium/Lithium Heparin / Potassium EDTA

Minimum Specimen Requirements

150 uL



Approval is not required

CPT Codes


Shipping and Contact Information

The Hospital for Sick Children
Rapid Response Laboratory
170 Elizabeth Street, Room 3642
Toronto, ON
M5G 2G3
Phone: 416-813-7200
Phone: 1-855-381-3212

Reference Range

<4d - <1y : 1.3-6.3 nmol/L (Male & Female)
1-<12y : 1.7-2.9 nmol/L (Male & Female)
12-<15y : 1.5-2.7 nmol/L (Male & Female)
15-<17y : 1.5-2.4 nmol/L (Male)
15-<17y : 1.4-2.2 nmol/L (Female)
17-<19y : 1.6-2.1 nmol/L (Male & Female)