Free T4 shows the amount of active thyroid hormone available in your blood.
Free thyroxine, or free T4, is the unbound, active form of the main hormone made by your thyroid gland. Most thyroxine in your blood travels attached to proteins, but only the small free fraction can enter cells and do its work.
Thyroxine helps set the pace of your metabolism. It influences body temperature, heart rate, energy levels, and how your body uses fuel.
Free T4 is one of the most reliable ways to check how much thyroid hormone is actually available to your body. It is usually read together with TSH, the pituitary signal that tells the thyroid how hard to work.
A high free T4 can point to an overactive thyroid, with symptoms like a racing heart, weight loss, and feeling wired. A low free T4 can point to an underactive thyroid, with tiredness, weight gain, and feeling cold.
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 T4 (adults) | 12 to 22 pmol/L |
Source: LOINC 3024-7. Confirm against your own laboratory's range.
Your result shows whether your thyroid is producing the right amount of active hormone. Read alongside TSH, it helps tell apart an overactive from an underactive thyroid, and it can flag a thyroid issue before symptoms become obvious.
Levels can be affected by pregnancy, severe illness, and some medicines including amiodarone, heparin, oestrogens, and high-dose biotin supplements, which can interfere with certain assays. Tell your provider about any supplements.
Best read together with TSH and, when needed, free T3 and thyroid antibodies (TPO Ab, TgAb).
What does my Free T4 result mean? It reflects how much active thyroid hormone is available to your body. Higher or lower levels give clues about thyroid balance.
Do I need to fast? No. For consistency, many people test in the morning and before taking their daily thyroid pill.
What can affect my result? Biotin supplements, recent levothyroxine dosing, amiodarone, steroids, heparin, pregnancy, contrast dye, and acute illness can all impact results.
How often should I test Free T4? Your clinician will guide this. If medicine changes, retesting is usually done several weeks later to check trends.
How long do results take? Results are usually ready in about 7 days.
What should I discuss with my clinician? Share your symptoms, all medicines and supplements, pregnancy plans, and when you last took thyroid medication.
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