Total T3 blood test
Total triiodothyronine
In short
A typical adult total T3 result is 80 to 200 ng/dL. A high total T3 usually goes with an overactive thyroid, when TSH is usually low. Extra carrier protein, from pregnancy or estrogen, can also raise it. Always read your result against the range printed on your own report.
All the T3 thyroid hormone in the blood, bound and free.
T3 (triiodothyronine) is the most active thyroid hormone; total T3 counts the bound and free parts together. It is mainly used to check for an overactive thyroid. It is not a reliable test for an underactive one.
Is my Total T3 high or low?
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Typical range
| For | Range | Unit |
|---|---|---|
| Adults | 80–200 | ng/dL |
| Adults | 1.2–3.1 | nmol/L |
Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.
If your Total T3 is high
A high total T3 usually goes with an overactive thyroid, when TSH is usually low. Extra carrier protein, from pregnancy or estrogen, can also raise it.
Common reasons
- Birth control pills, hormone therapy or pregnancy, which raise carrier proteins
- For people on thyroid medicine, a dose above what the body needs
- Graves' disease, an immune condition that makes the thyroid overactive
- Thyroid nodules, small lumps that make extra hormone on their own
- Less often: a rare growth in the pituitary, the gland that makes TSH
If your Total T3 is low
A low total T3 is common during or after an illness. On its own, it is not a reliable sign of an underactive thyroid.
Common reasons
- A recent illness, surgery or hospital stay, which lowers T3 for a while
- Eating very little or fasting, when the body makes less T3
- Low carrier protein, for example with some kidney conditions
- Some medicines, including steroid medicines and some for heart rhythm or seizures
- An underactive thyroid, usually with a high TSH
What can throw it off
Illness, fasting, pregnancy and estrogen can all shift total T3, and biotin, a hair-and-nail supplement, can distort it on some lab tests.
Questions to take to your appointment
- 1Do my TSH and free T4 point the same way?
- 2Could my medicines, hormones or a recent illness explain it?
- 3Would a free T3 test tell us more?
Read together with
Doctors rarely read Total T3 alone. These usually sit next to it.
Quick answers
What is the total T3 blood test?
Total T3 (Total triiodothyronine): All the T3 thyroid hormone in the blood, bound and free. T3 (triiodothyronine) is the most active thyroid hormone; total T3 counts the bound and free parts together. It is mainly used to check for an overactive thyroid. It is not a reliable test for an underactive one.
What is a normal total T3 level?
For most adults, total T3 is typically 80 to 200 ng/dL. Some countries print it in nmol/L, so check the unit first. Labs differ a little, so the range printed next to your result is the one to go by.
What does a high total T3 mean?
A high total T3 usually goes with an overactive thyroid, when TSH is usually low. Extra carrier protein, from pregnancy or estrogen, can also raise it. Common reasons include birth control pills, hormone therapy or pregnancy, which raise carrier proteins; for people on thyroid medicine, a dose above what the body needs; Graves' disease, an immune condition that makes the thyroid overactive; and thyroid nodules, small lumps that make extra hormone on their own. A doctor reads it together with your other results and how you feel.
What does a low total T3 mean?
A low total T3 is common during or after an illness. On its own, it is not a reliable sign of an underactive thyroid. Common reasons include a recent illness, surgery or hospital stay, which lowers T3 for a while; eating very little or fasting, when the body makes less T3; low carrier protein, for example with some kidney conditions; and some medicines, including steroid medicines and some for heart rhythm or seizures.
What can affect my total T3 result?
Illness, fasting, pregnancy and estrogen can all shift total T3, and biotin, a hair-and-nail supplement, can distort it on some lab tests.
What should I ask my doctor about my total T3?
Questions worth taking to the appointment: Do my TSH and free T4 point the same way? Could my medicines, hormones or a recent illness explain it? Would a free T3 test tell us more?
What this page can’t do
It reads each number on its own.
Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.
It doesn't know you.
Your age, your medicines, how you feel and your last result all change what a number means.
It doesn't remember.
Close this page and your results are gone. That's on purpose: nothing was ever sent to us.
We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.
Vita: Health Coach on the App StoreSources
- Mayo Clinic Laboratories — T3 (triiodothyronine), total, serum
- MedlinePlus — Triiodothyronine (T3) tests
Stuck on a word? See the medical words. How we choose our sources. More about Vita Health Coach.