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FT4-Free Thyroxine Serum Test

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Free T4 Test Overview

T4 (thyroxine) circulates in body in a bound form with thyroxine-binding globulin and albumin.  Less than 0.3% of the total T4 is free fraction (FT4) and is the active form. Free T4 test measuring free T4 levels, more accurately reflect how the thyroid gland is functioning when checked with TSH.
Thyroid hormones are essential for growth and metabolism. Following are the symptoms of hyperthyroidism: weight loss, rapid heartbeat, tremors, sweating, anxiety, increased sensitivity to heat, etc. 
Whereas patients with hypothyroidism suffer from weight gain, fatigue, slow heart rate, increased sensitivity to cold, depression, dry and thin hair etc.

A thyroxine test or T4-Free Thyroxine Serum Test is used to diagnose thyroid conditions. The hormones produced by the thyroid gland help in controlling the way our body utilizes energy. Our thyroid is a tiny, butterfly-shaped gland. It is located at the base of our throat. The thyroid hormone also affects our weight, muscle strength, body temperature, heart health, and even our mood. When it comes to children, a thyroid disorder can affect their growth as well.


A T4-free thyroxine test measures the amount of thyroxine hormone in our blood. In case the level of T4 hormone in our blood is too little or too much, it is an indication that we may have thyroid disease.


T4 levels are measured using two different tests:


  • A free T4 test is used to measure the T4 levels directly in the blood. As per medical experts, this test provides more accurate information in comparison to the total T4 test.
  • The total T4 test is used to check the level of both free and found T4 together. This method is considered to be less accurate to check the working of our thyroid gland.

  The Free T4 test is done to:

  1. To diagnose thyroid disorders: The free T4 test is often used to evaluate thyroid function and to diagnose thyroid disorders such as hypothyroidism or hyperthyroidism.
  2. To monitor thyroid function: The free T4 test may be ordered to monitor thyroid function in people who are being treated for thyroid disorders.
  3. To assess the effectiveness of thyroid medication: If someone is taking thyroid medication, their free T4 levels may be checked to make sure the medication is working effectively.
  4. To assess fertility issues: The free T4 test may be ordered as part of an infertility workup, as thyroid disorders can affect fertility.
  5. To evaluate symptoms such as fatigue, weight gain, or weight loss: If someone is experiencing symptoms such as fatigue, weight gain, or weight loss, the free T4 test may be ordered to help diagnose or rule out a thyroid disorder as a possible cause.
  6. To monitor pregnancy: The free T4 test may be ordered during pregnancy to monitor thyroid function, as thyroid disorders can affect the health of the mother and the developing fetus.

Written by: Dr Vishal Wadhwa, M.D, D.N.B Microbiology, Medical Affairs

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FT4-Free Thyroxine Serum Test Price

Metropolis Healthcare is a leading diagnostics centre and pathology lab in India equipped with the latest state-of-the-art technologies that provides the FT4-Free Thyroxine Serum Test with a clear pricing structure.

The FT4-Free Thyroxine Serum Test Price in Mumbai is ₹ 360 .

We are committed to deliver accurate and quality results from the best labs in India with complete transparency regarding test cost and turnaround time. No matter where you are, we strive to offer patients high-quality service that is affordable and accessible.

Frequently Asked Questions

Free T4 test is done along with TSH to
1. Diagnose thyroid disorders both overt & subclinical
2. Monitoring patients on thyroid replacement therapy
In a very small group of patients only T3 & FT3 is increased.
In pregnancy due to increase in thyroglobulin and decrease in albumin may cause increase of T3 & T4 levels, without actually impacting body functions hence testing FT3 and FT4 is more representative

Free T4 test measures levels of FT4 hormone in blood

Free T4 test requires a blood sample. A tourniquet (elastic) band is placed tightly on the upper arm. The patient is then asked to make a fist. This helps in the build-up of blood filling the veins. The skin is disinfected before needle insertion and the blood sample is collected in vacutainer.

High TSH & high T3/FT3 and T4/FT4: Thyroxine replacement therapy; pituitary adenoma; drugs like heparin, amiodarone, beta blockers, steroids; neonates; resistance to thyroid hormones
High TSH & low T3/FT3 and  T4/FT4: Autoimmune thyroiditis, thyroidectomy, post-radiation, iodine deficiency, thyroid infiltrating tumour/ amyloid
Low TSH & Low T3/FT3 and T4/FT4: Central hypothyroidism, non-thyroidal illness
Low TSH & High T3/FT3 and FT4: Grave's disease, toxic multinodular goitre, toxic adenoma, thyroiditis, drugs, hyperemesis gravidarum & hydatiform mole, congenital hyperthyroidism

In most cases, no special preparation is required for this test. Make sure to inform your healthcare professional about any medicines or supplements you are taking as they can affect the results of the test.

There is little to no risk associated with a T4-Free Thyroxine test. You may experience slight pain or bruising at the injection site, but the symptoms disappear fast.

If you have taken a T4-Free Thyroxine test, the results will be reported as free T4. T4 levels lower than normal can indicate hypothyroidism, thyroiditis, or congenital hypothyroidism. On the other hand, higher than normal free T4 levels can be a sign of hyperthyroidism, thyroiditis, toxin thyroid nodule, toxic goitre, or a non-cancerous tumour in the pituitary gland.

Certain medications like phenobarbital can have an impact on your free T4 levels. Besides this, severe cases of chronic ailments such as cirrhosis of the liver or chronic renal failure can also affect your T4-Free Thyroxine test results.

The normal range for free T4 ranges between 0.9 and 2.3 nanograms per decilitre, or 12 to 30 picomoles per litre. However, the normal value ranges may differ slightly depending on the laboratory where you get your test done.

The normal range for free T4 classified according to age are as follows:

o   Children/adolescents: 0.8-2 ng/dL

o   Adults: 0.7-1.8 ng/dL

o   Pregnant women: 0.5-1 ng/dL

Normal TSH with normal T4 indicates normal thyroid function. However, high TSH along with a normal T4 means we are at a higher risk of developing underactive thyroid. On the contrary, low TSH levels with high T4 levels mean that our thyroid gland is overactive.

Your healthcare provider may recommend you to get a T4-Free Thyroxine serum test if you show any signs of thyroid disorder, such as:


  • Symptoms of underactive thyroid
  • Symptoms of overactive thyroid
  • Abnormal findings in other types of thyroid tests, like T3 or TSH
  • Hypopituitarism – a condition where the pituitary gland fails to produce enough hormones
  • Nodule or Lump in the thyroid gland
  • An irregular or enlarged thyroid gland
  • Problems getting pregnant

Thyroid disorder is a hereditary condition. Therefore, your doctor may prescribe you a T4 test in case anyone in your family has a thyroid disorder. You may also require a T4 test if you show any symptoms of too little or too much thyroid hormone.


Common symptoms of hypothyroidism include:


  • Weight gain
  • Fatigue
  • Dry, thinning hair
  • Dry skin
  • Over-sensitivity to cold temperatures
  • Heavy menstrual periods or fertility issues
  • Depression
  • Slow heart rate


Symptoms of hyperthyroidism include:

  • Nervousness, irritability, and anxiety
  • Weight loss
  • Muscle weakness
  • Shaky hands
  • Over sensitivity of heat
  • Arrhythmia
  • Goiter
  • Frequent bowel movements
  • Fatigue and trouble sleeping

o   Free thyroxine

o   Free T4

o   Thyroxine screen

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