Triiodothyronine (T3) Test

Hypothyroidism, Hyperthyroidism, Hashimoto's thyroiditis, Thyroid cancer

For the human body to function, it needs energy. This energy is generated from food by the process of Metabolism. Metabolism is assessed by the basal metabolism rate (BMR). The thyroid gland secretes hormones that have a direct impact on the BMR levels. T3 and T4 hormones by the thyroid gland play a vital role in metabolism, growth and development.

The T3 test is used in the diagnosis of clinical as well as subclinical thyroid disorders.

The thyroid gland is an endocrine gland present in the human body. It is situated at the lower front part of the neck. It regulates bodily functions such as metabolism, energy production and mood. The thyroid gland produces T3 and T3 under the effect of thyroid-stimulating hormone (TSH).

T3 and T4 hormones are produced by the thyroid gland using iodine obtained from meals.

T4 or Tetraiodothyronine is generated entirely by the thyroid gland.

T3 is Triiodothyronine, which is created by reducing the iodine from T4.

T3 and T4 are present in the blood in two forms.

• Bound form
• Freeform

Two blood tests that are part of a T3 test report:

• Total T3

Total T3 measures the total amount of Triiodothyronine in the blood. This T3 test report includes the amount of T3 bound to blood proteins.

These proteins help in the transport of the hormone.

• Free T3

Free T3 test report measures the thyroxine that is not bound to proteins. Free T3 is the portion of T3 that is available to other body cells for functioning.

T3 hormone becomes abnormal before T4 and returns to normal levels later than T4. Hence, the free triiodothyronine (FT3) test determines whether the thyroid gland is functioning optimally or if there is some thyroid disorder. The T3 test is more useful to detect hyperthyroidism.

If the symptoms point to a thyroid problem, the doctor may prescribe a T3 test. 

The Thyroid gland can be either hyperactive or underactive:

• Hyperthyroidism is a condition in which the thyroid is more active. In this hyperactive thyroid condition, a person may experience

• Weight loss
• Rapid heart rate
• Increased perspiration
• Hair fall
• Skin darkening
• Swelling in the neck

• Hypothyroidism is a condition where a person has an underactive thyroid gland. Hypothyroidism symptoms include

• Weight gain
• Weariness
• The feeling of being cold
• Carpal tunnel syndrome
• Vitamin deficiencies due to poor metabolism

Thyroid disorders can have severe complications. The proper diagnosis and timely treatment are essential to avoid these complications.

Thyroid diseases are endemic in certain parts of India where there is a lack of naturally available iodine. Goitre or hyperthyroidism can develop due to a lack of iodine in the diet. T3 and T4 are common deficits in the sub-Himalayan region. It is a crucial test to have during and before pregnancy since poor thyroid function might impact the growth of the foetus.

Other names of the T3 test:

• Thyroxine
• Total T3 concentration
• Thyroxine screen
• Triiodothyronine

What does the T3 test or measure and whom is this prescribed?

The T3 test measures the levels of bound T3 hormones in the blood sample.

T3 test becomes a part of the prescription advised by a doctor in people with symptoms of low or high thyroid hormones.

The T3 test is indicated if a person is experiencing the following symptoms:

• Unexplained weight loss or weight gain
• Lack of energy or restlessness
• Constipation or diarrhoea
• Oversensitive to cold or hot
• Hairfall, brittle hair
• Swelling, lump in the throat
• Laziness
• Cramps in the hands and feet
• Tremors in the hands
• Puffiness
• Bulging of the eyes
• Insomnia or excessive sleepiness
• Anxiety
• Irritability
• Mood swings
• Depression
• Increased or decreased heartbeat
• Irregular menstrual cycles

T3 test along with T3 and TSH is advised for people with a high risk of thyroid disorder. It includes:

• People with a family history of autoimmune illnesses.
• People with diabetes.
• For people who have had neck surgery, the thyroid gland might be affected in post-surgical conditions.
• People undergoing radiation therapy or chemotherapy too could be at risk of thyroid dysfunction.
• People with psychiatric disorders need screening for thyroid profile.
• Newborn babies with chromosomal anomalies.

The normal levels of T3 are mentioned in the table below.

The T3 normal range in pregnancy

The T3 normal range in newborn

The T3 test values are in two forms

• Total T3
• Free T3

Various metabolic dysfunctions are related to increased or decreased amounts of T3 in the blood. Diagnosis of these conditions cannot be based only on abnormal T3 test values.

For proper diagnosis, the T3 results would be part of the Thyroid Profile Test and the results put together would lead to a possible diagnosis.

T3 levels might potentially be affected during pregnancy. The obstetrician may recommend more tests if T3 levels are abnormal during pregnancy.

An abnormal level of T3 means some underlying cause that is affecting T3 values.

A low value in the T3 test means

• Dietary issues

Iodine is essential for the production of T3. A diet lacking in iodine can affect T3 synthesis.

• Prolonged fasting

Fasting involves a diet that does not contain salt. Salt is a rich source of iodine. Prolonged fasting affects overall thyroid hormones due to the lack of iodine.

• Malnutrition

Malnutrition is a condition where the person lacks both major and minor nutrients in their diet. The deficiencies of nutrients such as iodine, iron, selenium and zinc may affect T3 values.

• Iodine deficiency

Iodine is an element that is essential for thyroid hormone production. The human body does not synthesise iodine. Iodine has to be consumed through food substances in the diet. Decreased amount of iodine in the body leads to a reduction of T3 levels.

• Hypothyroidism

Hypothyroidism is a condition where thyroid production of thyroid hormones T3 and T3 becomes low. In hypothyroidism, the thyroid gland is in an underactive state. Low thyroid hormones reduce the overall basal metabolic rate.

• Pituitary disorders

Secondary hypothyroidism can develop due to pituitary disorders. The pituitary gland secretes a hormone called thyroid-stimulating hormone (TSH). TSH is essential for the production of T3 and T3.

Lack of TSH could be a potential cause for lowered T3 levels.

Increased T3 levels mean some underlying cause that is affecting T3 levels.

Elevated value in the T3 test mean

• Hyperthyroidism

Hyperthyroidism is a condition where the thyroid gland produces an excess T3 and T3.

Hyperthyroidism increases the overall basal metabolic rate.

• Thyroiditis

Thyroiditis is a condition characterised by swelling and inflammation of the thyroid gland. Thyroiditis can increase or decrease thyroid hormone production. An advanced phase is known as thyrotoxicosis.

• Toxic multinodular goiter

Toxic multinodular goitre is a disorder characterised by enlargement of the thyroid gland due to iodine deficiency or excess iodine or toxin. Some autoimmune diseases could also be a cause of multinodular goitre. The goitre affects levels of thyroid hormones.

• Excess iodine

Consumption of iodised salt affects the thyroid gland and its function of producing thyroid hormones T3 and T3.

• Increased dose of thyroid replacement medication

In low T3 and T3 levels, people are advised to hormone replacement therapy for a short duration. These therapies, if prolonged or if taken in high doses, can lead to low T3 levels.

The T3 test results are based on the analysis of a blood sample. It is a straightforward blood sample test and does not require any additional preparation or fasting.

Test Preparation

The T3 test procedure requires no specific preparation as it is a simple blood test.

The T3 test procedure does not require fasting. Before the T3 test, inform the doctor about ongoing medicines. The T3 test procedure lasts for 5 minutes.

What are the parameters included in the test?

The T3 test chart includes two parameters. The T3 test values give an idea about the decrease and increase in the T3 values.

The T3 test chart includes

• Total T3
• The T3 test result gives an idea about the functioning of the thyroid gland. If the value of the T3 test chart is on the higher side or lower side, it is an indicator of a thyroid disorder.

How frequently should you take this test?

Hypothyroidism or Hyperthyroidism is a chronic disease. In case of confirmation of diagnosis with a T3 test, treatment has to be started. Usually, an endocrinologist will prescribe the medicines for the same.

Since it is a chronic disease, high or low levels of T3 treatment will take time to change. Therefore, the doctors repeat T3 values every three months to monitor the levels and modulate the treatment strategy accordingly.

This three-month check-up will reveal whether the T3, both Free and Bound, has increased, decreased or remains the same. In the case of a healthy range of the T3 test results, the test may be repeated annually just as a screening routine check-up.