Thyroid hormones are important in maintaining normal body metabolism. These hormones consist of T3 (triiodothyronine) and T4, which are so named based on the number of iodine molecules attached to the thyronine molecule. Most people with thyroid gland disorders take T4 in the form of medications like Levoxyl, Synthroid, or levothyroxine, which help regulate your metabolic rate, promote weight control, control your energy and mood, as well as your cholesterol and other aspects of health.

Very few people know about T3, which is actually the active hormone. In fact, the body converts T4 to T3 hormone by removing one of the iodine molecules to attain normal thyroid function.

What Is T3?

The thyroid is a large gland situated in just below your Adam’s apple in the neck. It produces proteins and regulates the way your body uses energy and how your body reacts to other hormones. Your thyroid produces T4 and T3 hormones, which help control your body metabolism, heart rate, andtemperature.

T3 is a naturally occurring thyroid hormone that is important for normal metabolism. In some individuals, the body may not produce enough T3for some reasons. In these cases, the affected individuals must take Liothyronine, a T3 hormone used to replace the natural thyroid hormone of the body.

Also known as liothyronine, T3 plays an important role in the chemical makeup that controls almost every physiological process in the body, including growth, metabolism, and physical development. T3 hormone also plays a vital function in bone growth and development as well as in the production of chemicals in the central nervous system called neurotransmitters. In addition, T3 has a direct effect on embryonic and fetal growth. As a powerful hormone, T3 acts on the body to boost basal metabolic rate, protein synthesis and sensitivity to catecholamines. It promotes proper growth and maturation of all body cells by regulating carbohydrate, protein, and fat metabolism, which in turn affects how cells use energy.

T3 (liothyronine) improves your body’s energy and oxygen utilization, which is important to preserve life. Liothyronine is a powerful thyroid hormone that is necessary for functioning of almost every major organ in the body except the spleen and the testes. In contrast, T4 or thyroxine hormone, is much less active, and has to be converted to T3 when the body needs it.

What Is T3 Test? What does it Show?

A T3 test measures how much of this thyroid hormone you have in the body. While most of your T3 is bound to protein, some molecules circulate freely in the blood. The T3 blood test measures both bound and unbound or free T3, also known as the T3 total test. By taking a T3 blood test your doctor can determine if you have a thyroid problem.

Your doctor will order a T3 blood test if he/she suspects a thyroid problem, which include:

• Hyperthyroidism (overactive thyroid that produces too much hormones)
• Hypopituitarism (when your pituitary gland does not produce normal amounts of hormones to stimulate your thyroid)
• Primary/Secondary hypothyroidism (underactive thyroid does not produce normal amount of thyroid hormones)
• A disorder called thyrotoxic periodic paralysis (when the thyroid produces high levels of hormones, resulting in muscle weakness)

What Do the Results Tell?

A T3 blood test may tell if you have a normal T3, low T3 or high T3 levels. Based on your history, physical examination and laboratory exams, a T3 test may help a doctor determine your condition.

Normal T3 Levels

A normal T3 test result typically ranges from 100 to 200 nanogram per deciliter (ng/dL). A normal result does not necessarily mean that your thyroid function is normal. Your doctor may need to measure your T4 and thyroid stimulating hormone (TSH) level to confirm if you do not have a thyroid problem.

High T3 Levels

T3 levels are usually elevated during pregnancy or if you are have a liver disease. High T3 levels may also indicate thyroid problems such as:

• Graves’ disease (autoimmune disease)
• Hyperthyroidism
• Silent thyroiditis
• Toxic nodular goiter (thyroid gland enlargement due to malfunctioning thyroid nodules that produce too much thyroid hormone)
• Thyrotoxic periodic paralysis
• Thyroid cancer, which is also associated with high proteins in the blood

Low T3 Levels

Abnormally low T3 levels may suggest any of the following:

• Chronic illness
• Hypothyroidism
• Starvation

T3 tests are usually not taken alone, but combined with other tests such as T4 and TSH tests, as well as other tests to confirm a diagnosis.

Possible Risks of T3 Test

What is T3 test risk? A t3 blood test is taken by drawing blood from your arm vein. This is a simple procedure but you may feel some discomfort. Minor bleeding and bruising may also occur. In some people, light-headedness occurs, but fainting, infection, inflammation or excessive bleeding is rare.