free t4 (ft4) - free thyroxine Test

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free t4 (ft4) - free thyroxin test

The thyroid is a small butterfly-shaped gland located in the neck region and is responsible for various functions of the body including metabolism and growth. Thyroxine (T4) is one of the two major hormones (the other called Triiodothyronine) produced by the thyroid gland.

T4 is either free (not bound) or protein-bound (bound to thyroxine-binding globulin) in the blood. The free form of T4 is biologically active, therefore monitoring and ascertaining concentrations of free thyroid hormone is of diagnostic value. Free Thyroxine is needed for the body tissues, its growth and replacement.

what is ft4 test?

The T4 test measures thyroxin levels in the blood and helps control metabolism and growth. Since there are two types of T4 in the human body, two type of tests and essential. One is the FreeT4 test, and the other is the TotalT4 test.

Free T4 test is preferred than the TotalT4 test in most cases because it is what available in the blood for more use.

why do i need this test?

A free thyroxine test is ordered to analyze thyroid function, which helps detect hypothyroidism or hyperthyroidism and to asses hypothyroidism in newborn and aids in detecting female infertility. This test is more accurate as it is not affected by protein level.

A hyperactive thyroid (overactive thyroid gland function), hypoactive thyroid(low thyroid gland function) and hypopituitarism(under-active pituitary gland) are some of the disorders that affect the thyroid gland.

what other tests might i have along with this test?

The T4 blood test is taken along with freeT4 blood test. TSH, T3 and freeT3 are other tests taken along with it for accurate interpretation of the thyroid gland functioning.

what do my test results mean?

Pregnancy affects T4 test levels. Elevated T4 level indicates Hyperthyroidism or thyroiditis or goitre. It is also caused by too much of iodine in blood/ too much protein /germ cell tumours/ too much thyroid medication. Abnormally low-level T4 indicates hypothyroidism, iodine deficiency, dietary issues like fasting and pituitary problems.

what are the reasons to take the free t4 test?

General symptoms observed are:

Excessive amounts of T4 in the blood results in symptoms associated with hyperthyroidism such as:

  • Nervousness
  • Tremors of the hands
  • Weight loss
  • Insomnia
  • Puffiness around dry, irritated eyes
  • Increased heart rate
  • Anxiety
  • Skin dryness
  • hair loss

Insufficient amounts of T4, show symptoms associated with hypothyroidism and a slowed metabolism, such as:

  • Weight gain
  • Dry skin
  • Fatigue
  • Constipation
  • Anxiety
  • sensitivity to light
  • Irregular menstruation

Doctors generally ask to take TSH and T3 test also along with the T4 test. The pituitary gland that produces TSH(Thyroid stimulating hormone) stimulates the release of T3 and T4 by the thyroid gland.

Taking all three test namely TSH, T3 andT4 helps to understand the working of the thyroid gland better. Also, the test is taken later part of the treatment again to know whether the working of thyroid gland shows improvement.

how is this test done?

This test is a blood test where a sample is collected by inserting a needle through your vein.

does this test pose any risk?

Some risks may come with this test as infections are known to break with the use of needles, and you may experience bleeding, bruising, or a hint of pain. The site where you are injected may feel sore for a while once the blood sample is collected. Otherwise, there are no specific risks involved in the T4 blood test.

what might affect my test results?

The only variables which may affect your test results are your nutritional diet, lifestyle and any other existing medications you're currently on. Please inform your doctor if you're using any supplements or prescription medications before you take this test.


sample required

Specimen type: Serum(Blood Sample)

Specimen collection procedure: Venipuncture(Collection of blood from a vein, usually from the arm)

how do i prepare for the test?

  • No Fasting Required.
  • No other special preparations required.

No special preparations are required for preparing for this test. You may continue eating different foods according to your diet and maintain the lifestyle you're used to now. However, the pills that you take affects the FT4 blood test to an extent. So it is always advisable to inform your doctor if you are currently on any medication.

The doctor might ask you to temporarily stop taking the pills to get the accurate results in the FT4 blood test. The medications that impact the test results are steroids, thyroid tablets like Thyronorm or Eltroxin, birth control pills and cancer-treating drugs. Inform the doctor if you take any of them and or any herbal treatment as well.

what is the test cost?

The FT4 test cost ranges from 350 to 450 rupees depending on the city.


Understanding results ofFree T4 (FT4) - Free Thyroxine

Reference RangeInterpretation
0.8 to 1.8 ng/dLNormal

‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’


T4 lab tests help the doctor conclude on the thyroid gland functioning.