Free T3 (FT3)
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About Free T3 (FT3)
T3 (Triiodothyronine) is one of the major hormones secreted by the thyroid glands (a small, butterfly-shaped gland situated in the lower front part of the neck). The T3 hormone comes in two different forms: bound and free. A bound T3 is attached to the protein, whereas a free T3 has no protein.
The free T3 test measures the amount of free T3 levels in the blood. If the levels of T3 are abnormal, it indicates a sign of thyroid disease.
This test is also known as Free triiodothyronine, FT3.
T3 plays a vital role in body’s metabolic rate, heart and digestive functions, muscle control, brain development and function, and maintenance of bones.
What is FT3 test used for?
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Anxiety
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Weight loss
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Tremors
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Increased heart rate
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Bulging of the eyes
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Insomnia (trouble sleeping)
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Fatigue
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Low tolerance for heat
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More frequent bowel movements
Who should get tested?
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Older than 40 years of age
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Have a thyroid problem
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Have a family history of thyroid diseases
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Have type 1 diabetes
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Have pernicious anaemia
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Have primary adrenal insufficiency
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Consume lots of iodine-rich foods
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Take medicines that contain iodine
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Recently pregnant or had a baby
Preparation for the test
You don’t need any special preparations to take the free T3 test. It is a simple blood test that involves the collection of your blood sample by inserting a needle in the vein in your arm. After sufficient blood is collected, the needle is taken out, and a cotton ball or piece of gauze is held at the site of needle insertion to stop the bleeding.
The whole procedure usually takes less than a few minutes.
Please tell your doctor if you are taking any medicines such as thyroid medicines, multivitamins, corticosteroids, etc., before undergoing this test, as certain medications interfere with the accuracy of the test results.
Interpretation of Results
The normal ranges for healthy individuals as per their age are as shown in the below table.
| Age group | Normal ranges – picograms per millilitre (pg/mL) |
|---|---|
| Infants up to 3 days old | 1.4-5.4 |
| Infants up to 4 to 30 days old | 2.0-5.2 |
| Infants (babies) 1 month to 1-year-old | 1.5-6.4 |
| Children 1 to 6 years old | 2.0-6.0 |
| Children 1 to 7 years old | 2.7-5.2 |
| Children 12 to 17 years old | 2.3-5.0 |
| Adults 18 to 99 years old | 2.3-4.1 |
Deviations from the normal ranges:
Any deviations from the normal ranges may indicate:
- Higher levels of T3 than normal may be a sign of:
- Overactive thyroid glands (Graves’ disease)
- Toxic nodular goitre
- Taking thyroid medicines or other supplements
- Liver diseases
- T3 thyrotoxicosis (rare)
- T3 levels are also elevated during:
- Pregnancy (most commonly in women who experience morning sickness during or near the end of their first trimester)
- Use of birth control pills or estrogen
- Lower levels of T3 than usual may be a sign of:
- Severe short-term or long-term illnesses
- Starvation
- Underactive thyroid gland (hypothyroidism)
- Thyroiditis (inflammation of the thyroid gland)
FAQs on Free T3 (FT3)
The test results of the free T3 test are usually available within 1-2 working days after the sample collection. At times, it might take a little longer than usual.
No. There are absolutely no major associated risks with a free T3 test for either the mother or the baby. It is a simple blood test that involves blood collection from a vein in your arm. However, all blood tests have negligible risks associated with them, such as feeling a slight sting or bruise at the site of sample collection, which usually resolves within a few minutes or hours.
It is common to have thyroid changes during pregnancy. These changes are usually very common, and most women don’t need to test for free T3. Nevertheless, your healthcare provider may suggest you undergo a free T3 test if you have:
- Symptoms of thyroid disease such as weight loss or gain, anxiety, tremors, sweating, etc.
- A history of thyroid disease.
- An autoimmune disease such as Graves’ disease or Hashimoto’s thyroiditis, etc.
- A family history of thyroid disease.
A few limitations of the free T3 test may include the following:
- Free T3 test results are not always reliable for detecting thyroid disease. Additional testing may be required to confirm the diagnosis of thyroid disease.
- External factors such as diet, certain illnesses such as diabetes, stress, and insufficient sleep for an extended period of time may also have an impact on test results.
- Some medications, such as thyroid medications, multivitamins, corticosteroids, birth control pills, female hormones such as estrogen, male hormones such as androgens, etc., may also interfere with the results of the free T3 test.
Free T3 (FT3)
