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T4, Free (fT4) details

What T4, Free (fT4) shows

Free T4 (fT4) measures the small, unbound, biologically active portion of thyroxine (T4) โ€” your main thyroid hormone โ€” available for your tissues to use, unaffected by fluctuations in binding proteins that can distort a total T4 result. It's one of the core tests, alongside TSH, used to diagnose and monitor both hypothyroidism (underactive thyroid, where free T4 tends to be low) and hyperthyroidism (overactive thyroid, where it tends to be high), and to guide and adjust thyroid hormone replacement medication dosing.

Normal ranges

Typical adult range

0.8โ€“1.8 ng/dL

Most labs report a range close to this

Hormunity optimal range

1โ€“1.5 ng/dL

A narrower functional target

Each lab sets its own reference range. Always compare your result with the range printed on your report, and review it with a healthcare provider.

Tests that include T4, Free (fT4)

Labcorp Not offered
Quest Not offered
Quest Not offered
Quest Not offered
Quest Not offered
Quest Not offered
ConsultationsConsultation

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Schedule a consultation with a Hormunity specialist. Weโ€™ll walk through every marker, interpret what it means for you, and map out the next steps for your care.

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