Free T3 shows the active thyroid hormone available to your cells and helps clarify thyroid function.
Free triiodothyronine, or free T3, is the unbound, active form of T3, the most potent thyroid hormone. Your body makes most T3 by converting T4 in the liver and other tissues.
T3 acts directly on cells to set your metabolic rate, affecting energy, heart rate, temperature, and mood.
Free T3 measures the active hormone that drives metabolism at the cellular level. It is most useful when an overactive thyroid is suspected, since free T3 can rise before free T4, and in some forms of hyperthyroidism it rises on its own.
A high free T3 points to an overactive thyroid. A low free T3 can appear in an underactive thyroid or during serious illness, when the body slows hormone conversion.
Aniva reads your result against research-backed ranges, not just the lab's wide normal. The reference shown below is specific to this biomarker.
Typical adult serum reference range, guidance only and assay dependent. Ranges vary by lab and method.
| Measure | Reference range |
|---|---|
| Free T3 (adults) | 3.1 to 6.8 pmol/L |
Source: LOINC 3051-0. Confirm against your own laboratory's range.
Your result shows how much active T3 your body has available. Read with TSH and free T4, it helps confirm and grade an overactive thyroid and adds detail when standard tests are unclear.
Severe illness can lower free T3 without thyroid disease, a pattern sometimes called non-thyroidal illness. Some medicines and high-dose biotin supplements can interfere with certain assays. Tell your provider about any supplements.
Best read together with TSH and free T4, and with thyroid antibodies when an autoimmune cause is considered.
What does a Free T3 result mean? It shows the amount of active thyroid hormone available to your cells. It’s interpreted with TSH and Free T4 for a fuller picture.
Do I need to fast for this test? No. Fasting is not required for Free T3.
What can affect my Free T3 level? Biotin supplements, thyroid medicines, amiodarone, steroids, heparin, and acute illness can shift results. Tell your clinician about all meds and supplements.
How often should I test Free T3? It depends on your situation. Monitoring is usually tied to symptoms, treatment changes, or follow-up after dose adjustments.
How quickly will I get results? Results are usually ready in about 7 days.
What should I discuss with my clinician? Share symptoms, medication timing, supplement use (especially biotin), pregnancy plans, and related test results like TSH and Free T4.
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