Total T3

Triiodothyronine or T3 is a hormone produced by the thyroid gland. The T3 blood test helps doctors diagnose thyroid disease. High or low T3 levels may indicate hyperthyroidism or hypothyroidism. The T3 test is most helpful in diagnosing hyperthyroidism. They are not very helpful in diagnosing hypothyroidism.

Forms of T3

There are two forms of the T3 hormone. 

• Bound T3 bound to protein 
• Free T3 is not bound to anything 

A test that measures both bound and free T3 is called a total T3 test.

Why T3 is done?

A doctor may order a T3 test if a child's symptoms or previous blood tests suggest thyroid dysfunction. The T3 test is particularly useful in diagnosing hyperthyroidism, a condition in which the thyroid gland produces too much hormone, causing symptoms such as increased heart rate, weight loss, shivering, and sweating.

Preparation 

No special preparation is required for this test. However, certain medications such as anticonvulsants, steroids, and oral contraceptives can affect results, so it's important to tell your doctor about any medications your child is taking.

Procedure 

A healthcare worker typically cleanses the surface of the skin with an antiseptic, places an elastic band (tourniquet) around the upper arm and applies pressure to inflate the vein with blood, and then draws blood from the vein. A needle is inserted into a vein (usually inside the arm, elbow, or back of the hand) and blood is drawn into a vial or syringe.After the blood is drawn, the needle is removed and the affected area is covered with cotton or a bandage to stop the bleeding.

High T3 levels

Higher than normal T3 levels usually indicate hyperthyroidism. Hyperthyroidism has several causes, including Graves' disease (an autoimmune disease), thyroid nodules, and thyroiditis (inflammation of the thyroid). 

Hyperthyroidism speeds up your metabolism and can be detrimental to your health. Symptoms of hyperthyroidism include: 

• Unexplained weight loss. 
• Tremors and/or nervousness. 
• Increased bowel movements. 
• Rapid or irregular heartbeat.

Low T3 levels 

Lower than normal T3 levels may indicate hypothyroidism. In addition, some people with severe hypothyroidism have high TSH levels and low free T4 levels, but normal T3 levels.

Normal T3 level

• Children aged 6 to 10: 104 – 183 ng/dL 
• Children aged 11 to 14: 68 – 186 ng/dL 
• Adolescents aged 15 to 17: 71 from 175 ng/dL
• Adults aged 18-99 years: 79-165 ng/dl.