Free Triodothyronine (FT3), Serum

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Test Details

  • FT3


Why T3 test?

The thyroid hormones basically regulate all the metabolic functions of the body and make all the cells in the body work. So basis your signs and clinical symptoms, the doctor may order TSH and T4 tests to assess thyroid function.

Who should be tested for T3?

A free T3 or total T3 test is ordered as part of the Thyroid Function Test. The T3 test is even more important when T4 levels are normal and if the symptoms point to hyperthyroidism. 

Signs and symptoms of Hyperthyroidism

  1. Increased Appetite
  2. Nervousness and feeling of restlessness
  3. Anxiety
  4. Unexplained weight loss
  5. Light sensitivity and visual disturbances
  6. Irregular menstrual cycle in women
  7. inability to concentrate
  8. weakness and fatigue
  9. Increased heartbeat
  10. Difficulty sleeping/insomnia
  11. fine, brittle hair and hair loss
  12. Unexplained Diarrhea in a few patients

Your healthcare provider will order T3 test are routinely ordered if you are on thyroid medication or under treatment for thyroid cancer.

More about T3

Other Names:  FT3, Triiodothyronine

The free T3 test or the Total T3 test is one of the important test of the thyroid panel and is used to evaluate thyroid function. This test measures the level of T3 or Triiodothyronine in the blood.

This test is especially important when your TSH levels are abnormal but T4 levels are not affected.

As we have seen earlier, triiodothyronine or T3 is one of the two important hormones produced by the thyroid gland. The thyroid gland produces T3 and T4 by absorbing iodine from the food. (iodised salt is a great source of iodine and is also found in many foods). Thyroid cells are the only kind of cells that can absorb iodine – iodine and tyrosine (amino acid) combine to form T3 and T4. 

T3 is an important thyroid hormone that regulates metabolism and ensures your body is able to perform essential functions properly. While most T3 in the bloodstream is bound to protein, some is unbound, or free. The free T3 test measures the active form of T3 that is not bound to protein. The total T3 test measures bound T3 and free T3 combined.

Free T3 or total T3 blood tests may be ordered to evaluate thyroid function if a thyroid disorder is suspected. They may also be used to evaluate pituitary gland problems, to assess the severity and type of thyroid disease, and to monitor treatment for a thyroid condition.

Reference Values for T3 test

T3 Reference Range

Male: 80 – 200 ng/dL


Non pregnant: 80 – 200 ng/dL

I Trimester: 105 – 230 ng/dL

II Trimester: 129 – 262 ng/dL

III Trimester: 135 – 262 ng/dL


Thyroid tests are never interpreted in isolation. Your healthcare provider will help you to assess your report basis your clinical findings. Below guide is a representation from medical findings.

Normal Normal Normal Indicates  thyroid function
Normal or reduced Normal or reduced Reduced Normal adjustment in thyroid function due to illness (non-thyroidal illness)
Elevated Normal Normal Subclinical hypothyroidism; patient with hypothyroidism on treatment does not receive enough thyroid hormone – In this hypothyroidism, while there may not be any pressing symptoms, the person is at greater risk for elevated LDL cholesterol levels and increased risk of cardiovascular disease
Elevated Reduced Normal or Reduced Primary Hypothyroidism: usually refers to when the problem is because of a defect in the thyroid gland itself
Normal or Elevated Elevated Elevated Central Hyperthyroidism is referred to a problem with the pituitary gland signals or thyroid hormone resistance which is a problem with the thyroid hormone receptor
Reduced Normal Normal Subclinical hyperthyroidism: this happens when a patient on treatment is being given too much thyroid hormone
Reduced Normal Elevated Hyperthyroidism that results from the thyroid gland making too much active thyroid hormone T3. This condition is quite uncommon and is also referred to as T3 toxicosis)
Reduced Elevated Elevated Hyperthyroidism resulting from the thyroid gland making too much thyroid hormones
Reduced Reduced Reduced When all three levels are reduced, it is because of a problem with the hypothalamus or pituitary signals that govern the thyroid gland and this also referred to as central hypothyroidism



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