Hormones
Total T3 (Triiodothyronine)
Also known as: T3
CONVERT & COMPARE
ng/dL
=
2.15
nmol/L
Reference ranges by source
Published adult intervals: 5, from 4 named sources, shown in ng/dL.
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SEX
AGE
RANGE
VISUAL
CITE
Ages 0–17 (CALIPER)
5 age- and sex-stratified entries from the Canadian Laboratory Initiative on Pediatric Reference Intervals.
SOURCE
SEX
AGE
RANGE
VISUAL
CITE
About Total T3 (Triiodothyronine)
A T3 test measures the level of thyroid hormone in your blood to help diagnose thyroid disease. The thyroid is a small, butterfly-shaped gland in the front of your neck. It makes hormones that control the way your body uses energy. The hormones affect nearly every organ in your body and control many of your body's most important functions. For example, they affect breathing, heart rate, weight, digestion, and mood.
The thyroid mostly makes two hormones, thyroxine (T4) and triiodothyronine (T3). T3 helps control your body's metabolism (how your body changes the food you eat into energy), heart rate, body temperature, muscle strength, and several other things.
There are two forms of T3 in your blood: free T3, the active form of the hormone that enters your tissues where it's needed, and bound T3, which attaches to certain proteins so it stays in your bloodstream. A total T3 test measures both bound and free T3. A free T3 test measures only the free form. Tests for T3 are usually done with other thyroid hormone tests, including a TSH test and a T4 test.
You may need a T3 test if you have symptoms of hyperthyroidism (an overactive thyroid). Symptoms can include anxiety, weight loss despite an increased appetite, shaky hands, sweating, fast or irregular heartbeat, frequent bowel movements, an enlarged thyroid gland (goiter), and trouble sleeping. You may also need this test if you take medicine for hypothyroidism (an underactive thyroid) to make sure your dose is correct, or if you had abnormal or unclear results on TSH or T4 tests.
Main source: MedlinePlus ↗
Useful for
Help diagnose hyperthyroidism, a condition in which your thyroid gland is overactive.
Help diagnose T3 toxicosis, a less common form of hyperthyroidism where TSH is low and free T4 is normal but T3 is high.
Help find the cause of hyperthyroidism.
Help diagnose pituitary disorders. The pituitary makes a hormone (TSH) that tells your thyroid to make T3 and T4. Abnormal T3 levels may be a sign that there is a problem with the pituitary gland.
Help monitor treatment for thyroid disease, including hyperthyroidism and hypothyroidism.
Main source: MedlinePlus ↗
Interpretation
Normal T3 levels alone do not rule out thyroid disease. But if your TSH and free T4 levels are also normal, you probably don't have a thyroid condition.
If you have high T3 levels with low TSH and high free T4, it may mean a problem with your thyroid gland (such as Graves' disease). If you have high T3 with normal or high TSH and high free T4, it may mean a problem with your pituitary gland.
If you have low T3 levels with high TSH and low free T4, it may mean your thyroid gland isn't making enough thyroid hormone (hypothyroidism). If you have low T3 with low TSH and low free T4, it may mean a problem with your pituitary gland.
Many things, including pregnancy, severe illness, and certain medicines, can affect T3 levels. Your provider may need to repeat the test or order more tests to find out what's causing abnormal results. If you have questions about your results, talk with your provider.
For general wellness information only. Talk to a clinician about your specific results.
Main source: MedlinePlus ↗
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Related biomarkers
More tests in the hormones category.
Sources
Last updated 2026-05-02
This page presents source-specific reference data and sourced explanations. For general wellness information only. This is not medical advice. For diagnosis or treatment of any condition, talk to a qualified clinician.