Test library
Triiodothyronine Blood Test
The T3 test measures triiodothyronine, a thyroid hormone that helps regulate metabolism, in the blood. It is used with other thyroid tests to evaluate abnormal thyroid function and possible T3 deficiency.
Order Triiodothyronine Hormone T3 Test
Order online and visit a local collection site, or choose an at-home kit where available. No referral and no insurance required.
Order Triiodothyronine Hormone T3 Test- Typical turnaround
- 1-3 business days
- Starting price
- From $39
- Results
- Confidential, online
Quick answer
The T3 test measures triiodothyronine, one of the hormones produced by the thyroid gland. T3 is the more active form of thyroid hormone and influences metabolism, heart rate, and body temperature. The test may measure total T3, which includes bound and free hormone, or free T3, which reflects the unbound, active portion. It is interpreted with TSH and T4 by a healthcare provider.
What this test measures
The thyroid gland produces two main hormones: thyroxine, called T4, and triiodothyronine, called T3. Most T3 in the blood is created when T4 is converted in tissues, and T3 is the form that acts most strongly on cells. Because T3 is largely bound to carrier proteins, free T3 is the fraction available to affect the body.
A blood sample is drawn from a vein, usually at the arm, and analyzed in a laboratory. Clinicians often order T3 with TSH and free T4 so the hormones can be read as a group. Total T3 measures both bound and free hormone, while free T3 estimates the active portion; the choice depends on the clinical question.
T3 results are not interpreted alone. Conditions such as illness, pregnancy, and some medications can shift thyroid hormone levels, and total and free values can move differently. A qualified healthcare provider reviews the result with symptoms and the rest of the thyroid panel before drawing conclusions.
- Total T3 (triiodothyronine)
- Free T3
- Reverse T3
- TSH (thyroid stimulating hormone)
- Free T4 (thyroxine)
- Total T4
- Thyroid peroxidase antibodies
- Thyroglobulin antibodies
Why people order this test
- Evaluate suspected hyperthyroidism or an overactive thyroid
- Assess possible T3 deficiency when other thyroid results are abnormal
- Monitor a known thyroid condition over time
- Distinguish between total and free T3 levels
- Follow up on an abnormal TSH or T4 result
- Investigate symptoms such as weight change, fatigue, or heat intolerance
How to prepare
No fasting is usually required. Some laboratories prefer a morning blood draw, and timing can matter if you take thyroid medication, so follow the instructions provided with the order and share a current medication list.
Understanding your results
Results are generally reported within one to three business days. The report shows total or free T3, which is interpreted with TSH and T4. Values outside the reference range do not diagnose a condition on their own; a qualified healthcare provider evaluates them in context.
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Frequently Asked Questions
What does the T3 test measure?
It measures triiodothyronine, a thyroid hormone involved in metabolism. The test may report total T3 or free T3.
What is the difference between T3 and free T3?
Total T3 includes hormone bound to carrier proteins plus the free portion. Free T3 measures only the unbound, active form.
Why is T3 ordered with other thyroid tests?
T3 is interpreted alongside TSH and T4. Reading them together helps a provider understand where a thyroid problem starts.
Do I need to fast?
Fasting is usually not required. Follow any timing instructions the laboratory provides.
Can medications affect T3 levels?
Yes. Some medications and supplements can change thyroid hormone levels, so sharing a current list with the ordering provider supports accurate interpretation.
Ready to get tested?
Order online and visit a collection site near you, or choose a mail-in kit. No referral and no insurance required.
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