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Thyroxine T4 Total

What is the T4 (thyroxine) total test?

T4 (thyroxine) total test is the one that checks the blood levels of the T4 hormone produced by the thyroid gland. The thyroid gland is one of the largest endocrine glands of the body, weighing about 15g to 20g in adults, present in front of the lower neck. It produces triiodothyronine and tetraiodothyronine or thyroxine, commonly known as T3 and T4 hormones, respectively.

These hormones serve in the major functioning of the body like growth, muscle strength, and specially increment of the body’s metabolism. A deficiency of thyroid hormones decreases the body’s metabolism by up to 40 to 50 percent. These hormones are secreted from the thyroid gland after being stimulated by TSH (thyroid-stimulating hormone), released by the master endocrine gland, the pituitary gland.

About 93% of the thyroid hormones released are T4, and 7% are T3. The thyroid gland also secretes another hormone, calcitonin, which maintains the blood and bone calcium balance of the body.

What is this test used for?

T4 (thyroxine) total test is used to diagnose many thyroid dysfunctions. This test measures total T4 levels (either bound or free) in the blood.

  • Abnormally high T4 levels indicate an increment in the size of the thyroid gland due to hyperplasia (increased cell division), which results in more production and secretion of T4. This is what usually causes hyperthyroidism.
  • Opposite to that, low T4 levels are possible because of the deterioration of the thyroid gland resulting in low amounts of T4, leading to hypothyroidism.
  • Some autoimmune diseases can also cause both conditions based on whether they stimulate the thyroid gland or destroy it.

Why and when do you need a T4 (thyroxine) total test?

You may be eligible for the T4 (thyroxine) total test if your doctor suspects any symptoms related to hyperthyroidism or hypothyroidism. It can also be ordered if you have any previous family history of thyroid dysfunction.
The most common symptoms that your doctor may consider for hyperthyroidism are:

  • Weight loss
  • Psychiatric disorders
  • Increased sweating
  • Tremor of the hands
  • Severe fatigue
  • Insomnia

The symptoms of hypothyroidism are:

What kind of sample is required?

A regular blood sample test examines the T4 levels. For the procedure, a healthcare professional will look for an appropriate vein and puncture it by gently pushing a needle into it; you may feel a slight tingle. Then the blood will be filled up in the tube attached to the needle. After that, the needle will be taken out, and pressure will be applied at the puncture site to stop bleeding.

Do you need to prepare for the test?

In case of any special preparations for the T4 (thyroxine) total test, your doctor will let you know in advance. But usually, there is no preparation or fasting required. However, some specific drugs such as steroids, birth control pills, cancer drugs, or even aspirin may alter blood T4 levels, so they should be avoided before the test.

Are there any risks to this test?

Drawing blood is usually a safe procedure and involves slight to no risks at all. If you have needle fear, you may feel a little uncomfortable. Besides that, there may be a little bleeding along with some bruising at the site of the puncture afterward, which is normal. Despite this, if you experience any of the below-mentioned symptoms, you may have to consult your doctor:

  • Excess bleeding
  • Lightheadedness or dizziness
  • Nausea
  • Infection
  • Inflammation in the punctured vein

What does the test result mean?

In adults, the normal range for the total T4 level is 5.0μg/dl to 12.0μg/dl. If your T4 (thyroxine) total test results are out of this range, you should talk to your doctor, who will look at your reports along with your symptoms; run some more tests for TSH and T3 levels if required, and then make the best diagnosis.

High total T4(thyroxine) levels:

If you have elevated T4 levels, you may be suspected of hyperthyroidism. In hyperthyroidism, your thyroid gland is overactive and produces more than normal amounts of thyroid hormones. Due to this, your total T4 levels become higher. Untreated hyperthyroidism can give rise to serious complications like:

Other than hyperthyroidism, the conditions which cause the thyroid gland to produce more hormones may be:

  • Graves’ disease (autoimmune disease)
  • Excess iodine intake
  • Diabetes
  • Pernicious anemia
  • Thyroiditis (inflammation of the thyroid gland)

Low total T4 (thyroxine) levels

Low T4 total levels may indicate a condition called hypothyroidism. In hypothyroidism, the thyroid gland cells are unable to produce a sufficient amount of thyroid hormones, so the body cannot run its normal functions. This is most likely caused by conditions like:

  • Past thyroid dysfunction (such as goiter)
  • Hashimoto’s disease (autoimmune disorder, which destroys the thyroid gland)
  • Certain medications
  • Too little iodine intake
  • Pituitary gland abnormality

Related tests:

  • TSH (thyroid-stimulating hormone) levels.
  • T3 levels.
  • TSI (thyroid-stimulating immunoglobulin) levels.
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