T4 (Thyroxine) Hormone Test

thyroxine t4 test

Last Updated December 20th, 2021

What is the thyroxine hormone and what is its role?

The thyroid plays an important role in the everyday functioning of the body. It secretes hormones that are responsible for aiding the daily functions of organs and controls the metabolism of the body. Amongst all the hormones the thyroid gland produces one of the
most important ones is known as thyroxine or T4. This hormone plays a very important role. The T4 or thyroxine hormone comes in two forms. They are as follows:

Free T4: This is a form of thyroxine hormone can enter tissues of the body wherever it is needed.
Bound T4: This form of thyroxine attaches itself to proteins and therefore is unable to enter tissues of the body.

Once the thyroid gland secretes T4 into the bloodstream, it is then converted into triiodothyronine. Hence after conversion, it helps manage the pace at which the body consumes energy. Since it affects body functioning, it is vital to maintain balanced levels of T4 hormones.

What happens when thyroxin levels are not maintained?

The thyroid gland produces a certain level of hormones for the everyday functioning of the body. The hormones produced by the thyroid gland including thyroxine is bound to the blood and sent throughout the body. The hypothalamus and the pituitary glands in the brain maintain the T4 and other hormone levels in the blood. If the gland releases too much of thyroxin it would lead to a condition called thyrotoxicosis.

It can lead to inflammation of the thyroid gland or a condition known as hyperthyroidism. Hyperthyroidism can lead to irregularities in heartbeat, make a person feel fatigued, cold, etc. Whereas if too little thyroxin is produced then it leads to a condition known as
hypothyroidism. In adults, hypothyroidism can lead to weight gain, low metabolism rate, fatigue, muscle stiffness tec, while in children it can bring about developmental issues. 

What is T4 testing?

There are various kinds of tests that help in providing a better understanding of how the thyroid works. One such test that many prospective patients take is known as T4 testing. This test helps healthcare physicians understand how his/her thyroid gland functions. The main aim of this test is to measure the levels of thyroxine produced by the gland. Since there are two forms that thyroxine takes, there are two types of T4 test.

Total T4 Test: This test calculates the total amount of thyroxine produced by the body including the thyroxine that attaches itself to proteins that help in transporting hormones through the bloodstream.

Free T4 test: This test measures the thyroxine hormone that has not attached itself and is available in the bloodstream. This is the thyroxine that is available for body use and is likely to affect the way various cells function throughout the body. This test is
considered to be more vital when it comes to understanding the functioning of the thyroid gland.

Some common names that a T4 test also goes by are free thyroxine test, total T4 concentration, free T4 concentration test, thyroxine screening test. 

Why undergo a T4 test?

There are various symptoms that manifest when a person is likely to have a thyroid-related illness. To better understand the problem and treat it with the right medication or treatment, it is important to undergo a T4 test. If the following symptoms are evident then it is important to undergo a T4 test.

– Fatigue
– Weight loss or gain
– Increasing heart rate
– Hair loss
– Trouble sleeping
Irregular menstrual cycle
– Constipation

How to prepare for a T4 test?

Since this is a simple blood test not much preparation is needed.The patient may be required to fast for several hours before the test, but this would be advised by their healthcare physician. If the patient is consuming medication for other diseases and conditions, the patient needs to be upfront about all the medication or treatments they are undertaking with their healthcare physician. Some of the medication may interfere with the test which is why it is important to
inform the healthcare physician conducting the test. Some medication that is likely to affect the test are as follows:

– Medication that contains androgen or estrogen-like birth control,
– Steroids
– Medication for thyroid function
– Medication for cancer treatment

What is the procedure of a T4 test?

The procedure for this test is a very simple blood test. The health care physician will need to collect a small vial of blood. The health care physician will first apply some antiseptic over the area where the syringe will be inserted. They may also put a small rubber band above to apply more pressure to the vein. Then a needle will be inserted into the vein and a small amount of blood will be collected, that will undergo testing. This may cause very little pain. The whole procedure will take place in 10-15 minutes.

How to interpret the results of a T4 test?

Since there are two kinds of test the interpretation of results varies on the kind of test. If the patient has taken a total T4 test, the ideal range within which the reading should fall between is 5.0 to 12.0 micrograms per decilitre (μg/dL). For a patient that has taken a free T4 test, the ideal range should fall within 0.8 – 1.8 nanograms per deciliter (ng/dL).

If it is a child that is undergoing this test the results vary according to the age of the child. Abnormal results (when test results are either too high or low) can lead to the diagnosis of other thyroid issues. In such cases, the patient may have to take other tests for better

When can you expect the test results back? 

The result will be given within 24-48 hours with which the patient can consult a health care physician for its interpretation.

What is the average price range for the thyroxine test in India?

The average price for a T4 test individual is between 200-800 Rs. If the patient opts to take other thyroid-related tests like T3, THS, etc, then the prices are likely to vary. 

How do thyroid hormones affect pregnancy?

During pregnancy, some women can experience certain changes with their thyroid hormones. The hormones produced by the thyroid gland play an important role in the development of the fetus. Due to the various physiological changes that pregnant women undergo, they can experience fluctuating thyroid levels that can at times lead to hyperthyroidism or hypothyroidism.

Some common thyroid-related issues that expecting mothers are likely to face during pregnancy are increased in blood concentration of T4 binding globulin, increasing demand for iodine, isolated maternal hypothyroidism, isolated maternal hyperthyroidism, iodine deficiency, etc. 

Is it T4 testing recommended during pregnancy?

For a healthy pregnancy, healthcare physicians may request expecting mothers to take a T4 test. This will help them in monitoring not only thyroid levels but also how it is likely to impact the development of the fetus as well. 

Is T4 testing recommended for children?

In rare cases when the healthcare physician or pediatrician notices certain signs or symptoms of thyroid-related disorders, they may prescribe a T4 test for a child. The procedure is the same as it is for adults. 


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