Total T3 (Total Triiodothyronine)

Clinical definition of the Total Triiodothyronine (T3) test
Triiodothyronine(T3) is one of the hormones produced by the thyroid gland. The total T3 test is the most common type of T3 blood test that measures both the bound and free forms of T3 in the blood. T3 exists in two forms in the blood.  The more abundant form, which is attached to proteins that help transport the hormone through the body and the less abundant form called T3 which circulates unattached. This test is performed as a part of an evaluation of thyroid function and measures the blood level of the hormone T3.

Why is the Total Triiodothyronine (T3) test done?
Total Triiodothyronine is carried out to check for thyroid dysfunction. It is useful in diagnosing hyperthyroidism, a condition in which the thyroid overproduces hormones.

What are the common signs/symptoms when the Total Triiodothyronine (T3) test is done?
Excessive amounts of total (T3) in the blood results in symptoms associated with hyperthyroidism such as:

  • Nervousness
  • Tremors of the hands
  • Weight loss
  • Insomnia
  • Puffiness around dry, irritated eyes
  • A fast heart rate
  • Trembling and sweating

Insufficient amounts of T3, show symptoms associated with hypothyroidism and a slowed metabolism, such as:

  • Weight gain
  • Dry skin
  • Fatigue
  • Constipation

What should I do before the Total Triiodothyronine (T3) test?

Specimen type

Specimen collection procedure

Preparatory instructions before the test *

Serum

(Blood Sample)

Venipuncture

(Collection of blood from a vein, usually from the arm)

No Fasting Required.

No other special preparations required.

*Subjects suffering from any illness or on oral or injectable medications are advised to consult their physician prior to requesting any tests or procedures.

How do I interpret my Total Triiodothyronine (T3) test results?

Reference Range*

Interpretation

Female

70 to 204 ng/dL

Male

70 to 204 ng/dL

Children

Boy(ng/dL)

Girl(ng/dL)

1-7 days

210-578

238-534

8-15 days

98-377

83-372

1-3 yrs

126- 253

138-217

4-6 yrs      

112-236  

148-261

7-8 yrs      

125-260   

143-270

9-10yrs     

114-213   

109-202

11 yrs       

141-220   

132-255

12 yrs       

139-235    

146-219

13 yrs      

134-262     

132-239

14 yrs       

128-220    

117-213

15 yrs        

112-224    

105-198

16 yrs       

115-219     

107-199

17 yrs        

76-164       

78-188

18-19 yrs   

79-152       

52-139

* Reference ranges may vary between labs depending on instruments used and method of establishment of reference ranges’’

Diseases/conditions related to the Total Triiodothyronine (T3) test

  • Graves’ disease
  • Hypopituitarism
  • Hypothyroidism - primary
  • Hypothyroidism - secondary
  • Thyrotoxic periodic paralysis
  • T3 thyrotoxicosis (Rare)
  • Thyroid cancer

Other tests related to the Total Triiodothyronine (T3) test

  • TSH
  • T4 
  • Thyroid Antibodies

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T3 (Total)

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