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The free triiodothyronine (FT3) test, most commonly referred to as the T3 test, analyses the amount of a hormone called triiodothyronine in the blood. T3 is a hormone secreted by the thyroid glands and is important for the metabolism of the body, including heart rate and temperature. T3 test is required in cases of symptoms like anxiety, weight loss, low tolerance for heat, and trouble sleeping. This test is most often done to diagnose hyperthyroidism, a condition in which the body produces too much thyroid hormone.
The other names are free triiodothyronine and FT3 test.
There is only one parameter.
The free triiodothyronine (T3) test analyses the levels of the free form of the T3 hormone.
The thyroid gland secretes the following hormones:
Triiodothyronine (T3)
Thyroxine (T4)
Calcitonin
Thyroid-stimulating hormone (TSH), also called thyrotropin, is a hormone secreted into the blood by the pituitary gland (a gland that is present in the brain). This directs the thyroid glands to produce and release the thyroid hormones (T3 and T4) into the bloodstream. Iodine is absorbed from the food that stimulates the thyroid glands to make thyroid hormones.
Thyroid hormones are essential for growth and metabolism. If the thyroid gland produces very high levels of T3 and T4 hormones, you may experience symptoms of weight loss, rapid heartbeat, tremors, sweating, anxiety, increased sensitivity towards heat, etc., and this is also known as hyperthyroidism. Decreased production of thyroid hormones results in hypothyroidism, which may cause weight gain, fatigue, slow heart rate, increased sensitivity to cold, depression, dry and thin hair, etc.
There is a feedback system in the body to maintain stable levels of the thyroid hormones (T3 and T4) in the blood. When the amount of thyroid hormone decreases, the pituitary gland is stimulated to release TSH. This high TSH, in turn, leads to an increase in the release of thyroid hormones (T3 and T4) from the thyroid gland and vice-versa.
The T3 hormone circulates in the blood in two forms:
Bound form: It is bound to the proteins present in the blood that prevent it from entering the body tissues.
Free form: This enters the body tissues where it is needed and thus is the active form.
The total T3 includes both the bound and the free forms circulating within the blood and may be affected by the amount of protein available in the blood to bind to them. The majority of the T3 hormone is formed from the T4 hormone, and a smaller fraction is produced directly by the thyroid gland. Free triiodothyronine (FT3) constitutes only 0.3% of the total T3 hormone. The two major proteins in the blood that the T3 hormone binds itself to the albumin and Thyroxine-binding globulin (TBG), also called Thyroid Hormone Binding Globulin (THBG).
Hence, the T3 hormone may be analysed as free T3 or total T3. The Free Triiodothyronine (T3) test is also a part of the Thyroid Profile test, which includes two more tests: Thyroid Stimulating Hormone (TSH) and Free Thyroxine (FT4).
4.26–8.10 pmol/L
This free T3 can be recommended when someone has an abnormal TSH test result. It can be recommended as part of the investigative workup when a person has symptoms suggesting hyperthyroidism, especially if the free T4 values are not elevated.
The signs and symptoms may include
Increased heart rate
Anxiety
Weight loss
Difficulty in sleeping
Tremors in the hands
Weakness
Diarrhoea (sometimes)
Light sensitivity and visual disturbances
The eyes can be affected by puffiness around the eyes, dryness, irritation, and, in some cases, bulging of the eyes.
Free or total T3 can sometimes be recommended at intervals to monitor a known thyroid condition or to help monitor the effectiveness of the treatment for hyperthyroidism.
No special preparation is required and fasting is not required for this test.
This test requires a blood sample.
A healthcare provider, who is also called a phlebotomist, usually performs blood draws, including those for FT3(Free T3) tests, but any healthcare provider trained in drawing blood can perform this task. These samples are sent to a lab where a medical laboratory scientist prepares the samples and performs the tests on analysers or manually.
You may expect the experience the following during the blood test or a blood draw:
You have to sit comfortably on the chair, and a healthcare provider will check your arms for an easily accessible vein. It is the inner part of your arm on the other side of your elbow.
Once the phlebotomist has located a vein, they will clean and disinfect the area with an alcohol swab.
They will insert a needle into your vein to draw a blood sample. They may feel like a small pinch.
After they insert the needle, the required amount of blood is drawn into a test tube.
When they have drawn enough blood for the test, they’ll remove the needle and hold a cotton ball or gauze on the pricked site to stop any bleeding.
They will apply a band-aid over the pricked site, and the blood collection is finished.
This process takes less than five minutes.
Once the phlebotomist has collected the blood sample, it will be sent to the laboratory for processing or testing. When the reports are ready, your healthcare provider will share the results with you.
These blood tests are very common, and they don’t carry any significant risks. You can have a slight pain like an ant bite when the needle gets inserted, and a small bruise might develop there.
This report is available via email or WhatsApp within 6 hours of the collection of the blood sample.
The free T3 or total T3 test will indicate whether the T3 is within the reference range, below normal, or higher than normal.
Free T3: 4.26–8.10 picograms per millilitre (pg/mL)
Total T3: 0.970–1.69 nanograms per millilitre( ng/mL)
The doctor will interpret the free or total T3 test results together with other tests, such as thyroid-stimulating hormone (TSH) and total and free T4.
Subclinical hypothyroidism and hyperthyroidism are the conditions defined by abnormal TSH test results with normal T3 and T4 levels. These subclinical conditions often cause no symptoms or only very mild ones. Some of these subclinical thyroid conditions can progress to outright hypothyroidism or hyperthyroidism over time.
4.26–8.10 pmol/L
Normal ranges might vary slightly among different laboratories. Some of the labs use different measurements or might test different samples. Speak to your health care provider about the meaning of your specific test results.
FT4, TSH, Thyroid peroxidase (TPO)
How do I book a FT3(Free T3) test at home?
Log on to www.orangehealth.in and submit your details. Our highly trained, professional, and vaccinated eMedics will be at your doorstep within 60 minutes or at the time booked by you.
Frequently Asked Questions on FT3 Test
The T3 test measures a thyroid hormone that is present in our bloodstream. Most of them exist bonded with proteins, while a small number are present unbounded. This unbounded form is known as free T3, which is readily available for use. Free T3 and total T3 tests evaluate the function of the thyroid gland and whether it is functioning well or not. This is the difference between the T3 and free T3 tests.
What is the normal range for free T3?
The normal reference range of free T3 in our bloodstream is 2.77–5.27 pg/mL. The reference range can vary slightly from lab to lab.
The symptoms of high T3 include:
Anxiety
Weight loss
Tremors in the hands
Increased heart rate
Bulging of the eyes
Trouble sleeping
Fatigue
Low tolerance for heat
Yes, there will be weight gain in hypothyroid people. If someone has low thyroid function, their TSH is high, the thyroid hormones known as T3 and T4 are low, and weight gain often occurs.
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