Thyroid: Difference between T3 and FT3

Overview of thyroid and its hormones

The thyroid gland, performed very essential functions for the human body. Few of them includes hormonal secretions and energy utilization control over the body along with body sensitivity towards hormones, hot and cold. This gland is present below Adam’s apple in the neck.

The thyroid gland produces hormones like triiodothyronine also known as T3, thyroxine — as T4. Together, both these hormones help in regulating the temperature, metabolism, and heart rate of your body.

Maximum of the T3, secreted in the body tends to binds to protein. However, there is some amount of T3 which doesn’t bind with protein which — as free T3 and it circulates in the blood freely being unbound. The most common type of T3 test, which is normally done to measure both the kinds of T3 available in the body, termed as the T3 total test.

By measuring the T3 total in your blood, your physician might be able to assess your condition in a better way and will be able to determine if case have any thyroid disorder.

Why is there a need for T3 tests?

T3 tests are required significantly to analyze the working condition of your thyroid gland. Your doctor will typically order a T3 test if they suspect a problem with your thyroid.

Following list includes the most commonly occurring thyroid disorders:

  • Hypothyroidism:

In this disorder, the pituitary gland is not able to produce normal amounts of pituitary hormones required for the proper functioning of various processes in the body. It can further be types of primary or secondary.

  • Hyperthyroidism:

In this disorder, the thyroid produces an excess of thyroid hormones than the usually required amounts.

  • Thyrotoxic periodic paralysis:

In this thyroid muscle weakness occurs because of high levels of thyroid hormones produced by the gland.

Each thyroid disorder, can cause several different symptoms. For example, you might experience mental problems like anxiety, or physical troubles like menstrual irregularities and constipation.

Other symptoms which might possibly appear include:

  • Fatigue and weakness
  • Abrupt weight gain or loss without any significant reason
  • Trouble sleeping
  • Sensitivity changes towards hot and cold
  • Skin troubles like dryness
  • Eye troubles like puffiness or bulging of eyes
  • Hair thinning or hair loss
  • Increased heart rates
  • Hand tremors

Thyroid T3

Also, in case you are already diagnosed with a thyroid problem then your physician might run T3 test to see if there are any changes in your condition or not. At times, the physician might also suggest getting FT3 or T4 or TSH test is done along with T3 for a more wider coverage in understanding the root cause of your disease.

While undergoing the T3 test no specific preparation, required. However, you must discuss with your physician in case you are taking any other medications for any ailments. Since few medications might affect the test results and hence your physician might even consider stopping your medications temporarily to avoid any false test results.

Following are the few medications that might affect your T3 test results:

  • Thyroid drugs in case you are already taking any for a thyroid problem.
  • Steroids
  • Contraceptives or birth control pills or any hormone pills including estrogens, and androgens etc.

Thyroid T3

A free or total triiodothyronine (T3) test, done to assess the functioning of the thyroid. It is, recommended mainly to help in diagnosing hyperthyroidism as well as monitoring the treatment efficacy of a person with any, pre-diagnosed thyroid condition.

What are FT3 and its need?

FT3 test, done to measure the level of free triiodothyronine. It is, done to confirm the hyperthyroidism and also to check the efficacy of the treatment during and after the drug therapy.  This test is also, known by the name free T3 test.

To get this test, done there is no pre-preparation requirement besides 10 to 12 hours of fasting prior the blood sample collection for a test. If any specific instructions, required that will be, shared by your physician depending on your case. But you must discuss your medical history with your physician before undergoing this test to prevent any false results because of medication therapy effects.

Recommended values for FT3

The normal range for test results of FT3 is 1.8 – 5.4 mcg/dl irrespective of age or gender.

Triiodothyronine (T3) is one of the main thyroid hormones and nearly 99.5 % of it nearly gets bound with the carrier proteins and keeps circulating in the blood. The protein which helps in its transportation is thyroxine-binding globulin (TBG). However, only the free or unbound triiodothyronine also called the free T3 is responsible for several biological actions. The concentrations of carrier proteins also vary in many clinical conditions, like in pregnancy.

In the normal thyroid function test, the changes in the concentration of carrier proteins and triiodothyronine level reflect free triiodothyronine concentrations remains constant. However, in an abnormal thyroid functioning case, this does not happen necessarily so, free T3 concentrations can help in correlating more reliably with the clinical status of the person rather than total triiodothyronine or T3 levels.

Wait does not give any results, so get a Triiodothyronine or T3 test along with FT3 to know if you, experiencing hyperthyroidism or not.


Hyperthyroidism disorder of the thyroid gland — main diagnosis and confirmation which is usually, obtained via T3 and FT3 tests. Following a good lifestyle along with regular exercise can help in preventing as well as controlling any pre-existing thyroid disorder. Where normal cases of hyperthyroidism might require antithyroid medications or even beta blockers for the treatment. On the other hand, some severe cases of hyperthyroidism might require radioactive iodine treatment or even surgery.

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