Free T4 shows the amount of active thyroid hormone available in your blood.
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Clinicians order Free T4 to clarify thyroid function, especially when TSH is out of range. It helps evaluate symptoms such as tiredness, weight change, or palpitations. Free T4 also supports monitoring and adjusting thyroid medication. You can test this marker with Aniva across Germany and Finland.
Clinicians order Free T4 to clarify thyroid function, especially when TSH is out of range. It helps evaluate symptoms such as tiredness, weight change, or palpitations. Free T4 also supports monitoring and adjusting thyroid medication. You can test this marker with Aniva across Germany and Finland.
High: May be seen with thyroid overactivity, thyroid inflammation, or too much thyroid medication. Pregnancy and some medicines or high-dose biotin can alter results; checking TSH and Free T3 and reviewing supplements can help clarify.
Low: May occur with an underactive thyroid, pituitary causes, severe illness, or medicine effects. Discuss symptoms and trends; repeating the test and pairing with TSH often helps interpretation.
Common factors that can skew results include high-dose biotin supplements; timing of your levothyroxine dose; amiodarone, glucocorticoids, and heparin; recent iodinated contrast; and severe illness. Pregnancy and estrogen therapy can change binding proteins and may affect some assays. Testing before your daily thyroid pill and at a similar time of day improves consistency.
Special situations (when to confirm or adjust): pregnancy, pituitary disease, known assay interference, or acute illness—consider repeat testing and review with a clinician.
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? Most labs report Free T4 within 1–3 business 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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