Thyroid Function Test : T3, T4, TSH Test

Thyroid Function Tests : T3, T4, and TSH

Thyroid function tests are a series of blood tests used to measure how well the thyroid gland is working. These tests include T3, T4, and TSH.

The thyroid is a small gland located in the lower part of your neck on the front side. It is responsible for helping to regulate many body processes, such as metabolism, energy production, and mood.

The thyroid produces two main hormones: 

  • triiodothyronine (T3) and 
  • thyroxine (T4). 

If the thyroid gland does not produce enough of these hormones, an individual may experience symptoms such as 

  • weight gain, 
  • lack of energy and depression. 

This condition is called hypothyroidism.

If the thyroid gland produces too many hormones, an individual may experience 

  • weight loss, 
  • high levels of anxiety, 
  • tremors, and 
  • a feeling of being high. 

This is called hyperthyroidism.

List of Thyroid function Test

TSH test: This is done to check the amount of TSH in the blood. TSH is a hormone produced in the pituitary gland, which tells the thyroid gland to produce the hormones T3 and T4 in the right amounts. The pituitary gland continuously produces and releases TSH into the blood.

T4 test: This test checks the amount of T4 in the blood. Levels of this hormone may increase as a result of pregnancy and oral contraceptives. Certain diseases and medications (to treat arthritis, asthma, or other health problems) can cause a drop in T4 levels. 

T3 test: If a person has hyperthyroidism despite a normal T4 level, he or she should undergo a T3 test to confirm the diagnosis. 

Thyroid antibody test: Thyroid antibodies are produced when the immune system starts attacking the thyroid gland. Measurement of thyroid antibodies may help diagnose autoimmune disorders such as Graves’ disease and Hashimoto’s disease.

What are the reasons to do a Thyroid Function Test?

A health care provider may recommend TFTs to diagnose several thyroid conditions, such as:

Hyperthyroidism (overactive thyroid)

Symptoms of hyperthyroidism include: 

  • Anxiety 
  • weight loss 
  • Increased heart rate 
  • Weakness 
  • Diarrhea 
  • Difficulty sleeping Eyes

Hypothyroidism (underactive thyroid) Thyroid

The symptoms of hypothyroidism are: 

  • Sudden weight gain 
  • Constipation 
  • Dry skin 
  • Fatigue 
  • Hair loss 
  • Cold intolerance 
  • Skin inflammation 
  • Irregularity in menstrual cycle in women 

Illness Graves’: an autoimmune disorder characterized by Hyperthyroidism Causes.

Hashimoto’s disease: An autoimmune disorder in which the thyroid gland is gradually destroyed.


How do you prepare for the Thyroid Function Test? 

This test usually does not require any special preparation. This can be done at any time of the day, and you do not need to be fasting to perform this test. However, some medications can affect the results of thyroid function tests, so it is best to tell your doctor if you are taking any prescription or non-prescription medicines. 

How are thyroid function tests done? 

To perform this test, a blood sample is taken from a vein in your arm with the help of a needle. The procedure is painless and non-invasive, but some patients may experience slight redness at the needle puncture site. Redness can be reduced by applying an ice pack to the affected area. 

Thyroid Function Test Results and Normal Values ​​Normal Results: 

The normal range for thyroid hormone levels is the following: 

  • TSH: 0.4-4.0 mU/L (million per liter) 
  • Free T4: 9.0- 25.0 pmol/L (picomoles per liter)
  • Free T3: 3.5-7.8 pmol/L 

Abnormal results: If the thyroid gland is not working properly, it can result in an increase or decrease in thyroid hormone levels. An increased level of TSH can be a sign of hyperthyroidism and a low level of TSH can be a sign of hypothyroidism. The TSH test will probably be done first. If it is abnormal, other tests will be done to get more clarity on your condition. 

High TSH levels can be caused by the following conditions: 

  • Hypothyroidism 
  • Dysfunction of the pituitary gland 
  • Inadequate doses of thyroid hormone medication to treat hypothyroidism. 

Low TSH levels may be caused by the following conditions: 

  • Hyperthyroidism 
  • The dosage of thyroid hormone medication for the treatment of hypothyroidism is excessive. 

In addition to TFTs, the following tests may be used to diagnose thyroid disorders: 

  • Ultrasound 
  • thyroid scan 
  • Radioactive iodine uptake test


Also, Read About Other Lab tests:


( Disclaimer: Information provided in this piece of article is purely for educational purposes only. All results must be clinically correlated with the patient’s data to make an accurate diagnosis.)

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