Thyroid: what is T4 and it’s ideal levels.

Overview of Thyroxine (T4) Test

Thyroxine, also known as T4, is one of the thyroid hormones. Abnormal levels of thyroxine test help to diagnose the thyroid disorders. The thyroid is a small, butterfly-shaped gland located near the throat. It makes hormones to regulate the various body functions like energy usage, body temperature regulation, weight control, muscle strength, and even moods. T4 binds with the protein and the remaining is available in the free form in the blood. In total T4 tests levels of both free and bound T4 are measured. A free T4 test measures the level of T4 in the blood and this test is more reliable for checking thyroid functioning than the other test. Excess of it in any tests indicates the thyroid disorder.

This test has few different names like free thyroxine or thyroxine screen, total T4 concentration, and free T4 or free T4 concentration.

Thyroxine is secreted as the main thyroid hormone into the bloodstream. It is an inactive form which gets conversion into active triiodothyronine in liver and kidneys. It further helps to regulate various body functions like of heart, brain, digestive system, bone maintenance, and muscle control.

T4 Test

Can too much of thyroxine cause any risks?

The excess of thyroxine release in the bloodstream is known as thyrotoxicosis. It might happen because of overactive thyroid or hyperthyroidism. An autoimmune disease like Graves’ disease or any benign tumor can cause it. Goiter can lead to thyrotoxicosis identification as well. Few symptoms might include weight loss, intolerance to heat, menstrual cycle disorders, hair thinning or hair fall, extreme fatigue, protruding eyes, and irregular heartbeats etc.

Can too little of thyroxine cause any risks?

It can cause hypothyroidism which might lead to underdeveloped brain and reduced growth before birth or during childhood. It can be because of some autoimmune disorder or poor iodine intake. Hypothyroidism in adults might lead to low metabolism. Its symptoms include fatigue, cold intolerance, weight gain, reduced fertility, poor memory, muscle stiffness, and depression.


Why should you go for a thyroxine T4 test?


Thyroid troubles are usually more common among women in their 30s or 40s. It might even be present as a hereditary disease. In case you notice anyone in your family with the disease than you must consider the thyroid test to ensure you are not yet captured by it. Also, in case you notice any thyroid related symptoms than you must consider getting the test done. Be sure of your health and get a Thyroxine Test done in the comfort of your home by just a click online and the technician will come to your place to collect the sample. This test can let you know if you have too little or too much or normal levels of thyroxine.


Below are few symptoms of overactive thyroid or hyperthyroidism:

  • Weight loss
  • Tremors
  • Anxiety

T4 Test

  • Increased heart rate or even palpitations
  • Trouble sleeping
  • Puffiness of skin or around eyes
  • Bulging of the eyes


Below are few symptoms of overactive thyroid or hypothyroidism:

  • Sudden weight gain
  • Extreme fatigue
  • Hair loss or thinning
  • Constipation
  • Cold sensitivity
  • Irregular menstrual periods


The symptoms might already be giving you a clue that its time to get the thyroxine test done. So do not delay and early diagnosis can only make its way to early treatment. Otherwise, delay in treatment might cause more complications which might not be easy to control life-long.


What is the procedure of a thyroxine test?

During this test a healthcare professional will take the blood sample from the arm vein, using a sterile needle. A prick of the needle will be felt upon needle insertion. The small amount of blood will be taken out preserved in the test tube or vial. It is then sent to a lab for evaluation. The entire test might take nearly five minutes.

No specific pre-test preparations are required for this test. You might only be asked to fast few hours prior the test by not eating or drinking anything to avoid any false test results.

No risk involvement is there in this test except little bruising or mild pain on the needle spot. The symptoms might eventually fade on their own without any extra care.

How to understand the results better?

The results might be shown in the form of total T4, free T4 index or free T4.

Following points must be kept in mind in order to understand it with ease:

  • The free T4 index uses a formula comparison of free and bound T4 levels.
  • High levels of any of the T4 values might indicate overactive thyroid condition or hyperthyroidism.
  • Low levels of any of the T4 values will certainly indicate underactive thyroid condition or hypothyroidism.
  • In case your T4 test results do not appear in the normal range, then your physician might recommend few more thyroid tests like T3 or TSH to confirm the diagnosis and its cause.
  • Hyperthyroidism further tests to confirm Graves’ disease can be recommended.
  • In hypothyroidism further tests to confirm Hashimoto’s thyroiditis, an autoimmune disease can be done upon recommendation.



Thyroid changes might happen during different stages of life like in pregnancy or in any diseased state. Sometimes they are not significant enough to get attention and at the other times, they become so noticeable via symptoms and then by a test. Chances of hypothyroidism are more than hyperthyroidism in pregnancies. So regular testing of T4 via Thyroid Test can assure your freedom from it.

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