Free T4
Free T4 is the main hormone your thyroid makes, in the form your body can use. It's usually checked alongside TSH to confirm whether the thyroid is under- or overactive.
Your reading
This app uses 0.8–1.8 ng/dL. High TSH with low free T4 points to an underactive thyroid; low TSH with high free T4 to an overactive one. Biotin supplements can distort the result.
What may help
- —Stopping biotin for a few days before the test
- —Taking thyroid medication consistently, at the same time each day, if you're on it
- —Reading it next to TSH rather than alone
When to talk to a doctor
If free T4 is outside the range, or TSH is abnormal at the same time.
Common questions
What is Free T4?
Free T4 is the main hormone your thyroid makes, in the form your body can use. It's usually checked alongside TSH to confirm whether the thyroid is under- or overactive.
What is a normal Free T4 level?
Daygo uses 0.8–1.8 ng/dL as the reference range. This app uses 0.8–1.8 ng/dL. High TSH with low free T4 points to an underactive thyroid; low TSH with high free T4 to an overactive one. Biotin supplements can distort the result.
How can I improve my Free T4?
Stopping biotin for a few days before the test. Taking thyroid medication consistently, at the same time each day, if you're on it. Reading it next to TSH rather than alone.
When should I see a doctor about Free T4?
If free T4 is outside the range, or TSH is abnormal at the same time.
Source: MedlinePlus (NIH). Reference ranges are standard adult intervals — your own lab may report a different range for your age, sex, or method. This isn't medical advice; always go by the range on your actual results and talk to a clinician about anything that concerns you.