Free T4
Also known as Free Thyroxine
The unbound, bioavailable fraction of thyroxine — the main circulating thyroid hormone.
Definition
T4 (thyroxine) is the main thyroid hormone produced by the gland, existing mostly bound to transport proteins. Free T4 is the unbound, bioavailable fraction that tissues can use. Measured alongside TSH and free T3 to characterise thyroid status — especially useful in central hypothyroidism where TSH may be misleadingly normal.
Read More
TSHThyroid-Stimulating Hormone
The pituitary hormone that drives thyroid output — the primary screening test for thyroid function.
BiomarkerFree T3Free Triiodothyronine
The bioactive thyroid hormone — small changes have outsized clinical effects.
Clinical ConceptThyroid AxisHypothalamic-Pituitary-Thyroid Axis
The feedback loop between hypothalamus (TRH), pituitary (TSH) and thyroid (T4, T3) — governs metabolic rate across tissues.
$149 panel.
A clinician reads it in 24 hours.
Order the Peptide Readiness Panel, draw at a Quest or LabCorp near you, and your clinician sends back a matched protocol with a confidence score.