Total T3 (total tri-iodothyronine)
What this test measures
Total T3 measures all the tri-iodothyronine in the blood, bound and free together. T3 is the active thyroid hormone, most of it made in the tissues from T4. Like total T4, this test is affected by the amount of carrier protein, so UK laboratories mostly report free T3 instead.
Why doctors request it
It is rarely requested on its own in the UK today. It appears on some older or overseas thyroid panels and in some research and private test settings.
What commonly pushes it up
- An overactive thyroid, including Graves disease
- Pregnancy and oestrogen-containing contraception or HRT, through higher carrier proteins
- Taking liothyronine or too much thyroid hormone replacement
- Some medicines, including amiodarone
What commonly pushes it down
- Any acute or long-term illness, because less T4 is converted to T3
- An underactive thyroid
- Fasting and low-calorie diets
- Low carrier proteins, for example in severe illness or liver disease
- Some medicines, including beta-blockers and steroids
Everyday reasons for a value outside the range
- It falls during any illness or period of dieting and recovers afterwards
- It rises on the combined contraceptive pill and in pregnancy without any thyroid change
- Laboratories use different assays with different ranges
About the sample
No fasting needed, although fasting and dieting lower it. Best read with TSH and free T4.
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Read my report freeThis is an educational summary of results you uploaded. It is not medical advice, a diagnosis or a treatment plan, and it does not replace the doctor who requested the test. If you are worried, or a result is marked outside range, discuss it with your doctor. Written and reviewed by a UK consultant physician. Reference ranges vary between laboratories.